2000 Suburban Transmission Disaster Need Help

Ok here is the story. Bought used 2000 3/4 ton 4x4 burb, 100,000 98,000 miles with check engine light on. Previous owner said that it had been on as long as he owned it (2nd owner) Said it was some transmission code but that it never gave him any problems. I had a couple of differnent mechanics scan it and gave the code that previous owner discribed. Test drove great..no problems...bought it, loaded it down with our six kids hit the road and then we found the problem. At highway speeds with our kids in the truck you could barely feel a type of shifting problem (like it was popping out of gear) very faint but noticible on uphill grades. We lived with the minor inconvience until the 4x4 gearbox when out that winter. We replaced the gearbox and then the transmission started blowing oil out the vent tube. As we looked into it harder we found a wire that had been cut going to the transmission. We hook the wire back up and the the service engine light goes off but the truck shifts incredibly hard (like an agressive shift kit) It doesn't do it when the truck is first started but as soon as it warms up...hold on. Our mechanic said it was the wire that locks the torque converter up into 5th and that we had been driving in 4th all this time and that addition pressure is probably the cause of the oil blowing out the tube. We have replaced the torque convertor, the valve body, a brake switch, the entire transmission with a jasper rebuilt, the computer that controlls the transmission and the problem still exist. When the wire is connected there is absolutely no codes. We have had a rep from a scanner company that lives local put it on the most upto date scanner and nothing... we are lost any help .. greatly appreciated

sounds like its just time for a rebuild bro, might be a broken band or synchro. Maybe a faulty speed sensor?

sounds like its just time for a rebuild bro, might be a broken band or synchro. Maybe a faulty speed sensor?
This is an automatic transmission, no synchronizers used! A speed sensor usually gives a code if not working properly and a broken band is a hard failure and generally gives a symptom that points right at that part. If this has had a complete rebuilt transmission installed, it MIGHT be safe to assume that it is working as designed. If that is the case and based on the external problems that have been noted I think I would look real hard again at all the wiring and inputs to the control module and transmission. Also, this is a 4 speed transmission, I don't know why the technician is refering to it as a 5 speed. Perhaps you need a more competent transmission technician and not a parts changer?

Whoa your right about the synchros my fault :runaround: And althought speed sensors usually set a code its not always. I had a dodge in the shop that would cut off when coming off the highway and stall. The speed sensor was giving a wrong reading so it wasn't bad just miscalculated. Its worth a look, thats all im sayin. Good luck.