Heated O2 Readyness Monitor

2000 Yukon, 6.0L, JBA Headers and exhaust, 70,000 Mi.
I know, I know I'm in the Tahoe page, but their about the same and I hope someone here might have the answer.
I had to clear a P1870 code from the ECM, this has the unfortunate side effect of clearing all of the Diagnostic Monitors. I've been through the suggested GM Drive Cycle several times but can't get the Heated O2 Sensor and Catalyst monitors to flip to complete. My OBDII reader shows a normal upstream O2 sensor graph and the downstream O2 sensor shows a nice lean exhaust. It hasn't set any other codes but I replaced the upstream sensors just in case, but no luck.
What is the computer looking for to complete the Heated O2 Sensor monitor. There is no circuitry in the heater to monitor current or voltage to the heaters, just a direct connection to the fuse. Does the computer look at the time for the sensors to go to closed loop, if so what is the time. If I leave the key on the sensors get warm, so the heaters are working, but is the steel tube exhaust conducting the heat away faster than the stock cast iron headers and extending the time to closed loop? Could I heat the area around the sensors with a torch before I do a cold start and hurry the transition time?
I need to get these completed so I can SMOG this thing and get to work on the transmission.
Any ideas? Thanks.

the heated O2 sensor current flow amplitude is monitored......on silverado I own 2000 5.3L.....it could be wires or the O2 sensors...in most cases...my vehicle up/down stream are the same since you got 2 new ones [O2] I would swap out down steam or check wires/connectors...are these oem exact replacements if not and the connectors are hacked to fit this may be your problem as well......

I found this, maybe it will help. Also, if it won't complete the test there should be a trouble code to indicate why but I'm not sure if it will turn on the SES light.

General Motors Driving Cycle
A complete driving cycle should perform diagnostics on all systems. A complete driving cycle can be done in under fifteen minutes.

To perform an OBDII Driving cycle do the following:

Cold Start. In order to be classified as a cold start the engine coolant temperature must be below 50°C (122°F) and within 6°C (11°F) of the ambient air temperature at startup. Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.

Idle. The engine must be run for two and a half minutes with the air conditioner on and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge "No Flow", Misfire and if closed loop is achieved, Fuel Trim.

Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until 88km/hr (55mph) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.

Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.

Decelerate. Let off the accelerator pedal. Do not shift, touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 32km/hr (20 mph). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.

Accelerate. Accelerate at 3/4 throttle until 88-96 km/hr (55-60mph). This will perform the same diagnostics as in step 3.

Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.

Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or brakes or shift gears.

Nope, no codes set, I replaced the upstream sensors with OEM but not the downstream. I can see the transition from open to closed loop, the upstream sensors begin to cycle regularly from about .2 to .8 volts and the downstream sensors move smoothly from a rich (.8V) reading to a lean (.2V) reading.
I've driven the GM Drive cycle completly and in parts many times and all the monitors have completed except the Heated O2 Sensor and Catalyst. I guess it's time to bite the bullet and replace the downstream sensors.
I would still like to know what the computer is looking for. It takes about 4 minutes for my system to go to closed loop, perhaps the system is looking for less time. My Olds Minivan go to closed loop in 1-2 minutes, perhaps the steel tube exhaust is keeping the sensors cool longer, since it's a larger diameter and a better heat conductor.
I'm really at my wits end, you used to be able to have two uncompleted monitors and still do the smog test. I'm sure it would pass if I could just get it in the door.
Thanks for the help.

Maybe you might try disconnecting the battery for a few minutes and starting over. I would think if there were a sensor problem you would get some sort of code, maybe not. By the way, do you know if the system was working before you cleared the codes?

Nope, sorry disconnecting the battery will just reset all of the monitors and I'll have to start over. I can clear codes with my ELM Scan OBDII decoder, it lets me read the condition of the monitors and view the OBDII data real time as well and view graphs of the O2 Sensor outputs. I cleared the transmission code P1870 which is what got me into this situation, so doing it again will not help.
I have JBA steel tube headers and exhaust on the truck, it could be that the larger diameter and better heat conduction of the tubes is keeping the sensors cool longer. It takes about 4 minutes for the truck to go to closed loop (my minivan goes closed loop in 1-2 minutes). If the computer wants the sensors to go closed loop in a certain time, that could be my problem. I may try preheating the exhaust near the sensors with a torch and see if they will close up earlier. I'll call JBA tomorrow and see what they say, I'll let you know what happens.

See my reply in your other thread, btw in the future stay with a single posting per forum rules, thanks.

Yes, I know disconecting the battery will clear everything but you will not be any worse off than you are now. My thinking is maybe the clear codes didn't go well and the PCM is confused or something. I have had scan tools not clear codes correctly in the past so it might be worth a try. Also, like maxwedge said, that option may not be supported on your vehicle. I'm sure if you ask the smog shop they can tell you what readiness tests need to be complete for your year and make. Also, I don't believe the O2 sensors will cause a delay in going to closed loop, I think it more depends on the engine temp. If there were a problem with the O2s when it went to closed loop it would trip a code and go back to open. Also, the rear O2s should read pretty lean for the most part if your cats are working.