truck shakes uphill

I have a 2000 Silverado 2500 4X4 with 236000 kilometers on it, I am having a problem and I am running out of ideas and money too. The problem is this, when I am going uphill the truck shakes pretty good, when I push the tow button it kicks it into overdrive, the RPM's go up and it works just great. I have changed the plugs, cleaned the EGR valve, replaced the Transfer Case Selection switch (I had to change it as the lights were not working all the time), with that, sometimes the service 4X4 light comes on. I have checked the ohm resistance on the sparkplug wires and they were all ok. I hooked my truck up to a scanner but the closest I could get to my truck was a 2004 model, I was told that it should be the same, the code thrown was B2725. I have also replaced all 3 drive shafts, like I said earlier, I am running out of ideas, please help. Also a few days ago I was towing my camper trailer and I was going up a fairly steep hill and my truck sounded like it was working pretty good, I noticed when I was going down the other side of the hill my service engine soon light came on.

Dave

You need to scan for history codes and also for misfire codes especially when you experience the problem, if this is not done all the attempts to fix this will be guess work, check fuel pressure also, especially under load. When you get into tow mode you are now out of o/d and lock up, which unloads the engine, thus no misfire occurs.

You need to scan for history codes and also for misfire codes especially when you experience the problem, if this is not done all the attempts to fix this will be guess work, check fuel pressure also, especially under load. When you get into tow mode you are now out of o/d and lock up, which unloads the engine, thus no misfire occurs.
Thank you, not to sound like a dolt but can you tell me how to do these things, how to scan for history codes, how to check fuel pressure under load, also I forgot to mention that when idling it has a slight hesitation.

Have you checked the Transmission mounting bracket on crossmember.
Seen these wear out and cause Shaking on other vehicles b4.
I think you can probably just try to move the tailhousing by hand to tell if its really bad.

Have you checked the Transmission mounting bracket on crossmember.
Seen these wear out and cause Shaking on other vehicles b4.
I think you can probably just try to move the tailhousing by hand to tell if its really bad.
Will do, thanks.