Last fall i had noticed the 1-2 shifts were very rough but thought nothing of it as the previous owner had the trans rebuilt, (less than 20k on it). They towed a small camper and i figured they had some upgrades done.
Well, now it feels like its searching for 1-2 when cold, over-revs then a rough shift. When warm the shift is better, but on hard acceleration the truck shudders. While cruising, every once in a while it feels the torque converter unlocks, however its too quick to notice a change in rpm.
I have been reading up on the tcc valve issue, i'm not sure if that was fixed during the overhaul and i'm not getting a P1870 code.

Could the tcc be at fault?

 

look at 3 and 4
FYI 4L60E common problems / failures | GM Truck Headquarters

 

Well, I had a chance to work on the truck. First I replaced the TPS, the one on there was completely shot. Took it for a test drive, the tuck shifted nice and smooth. Figured I had solved the problem. Next day, when cold, the transmission acted the same as before, shuddering on 1-2 shift. However with light driving around town the shudder disappeared when the transmission was warm.

This past weekend I replaced the valve body with an updated unit, and the 1-2 & 3-4 accumulator pistons. I took it for a test drive after I had allowed it to cool for a few hours after filling to try and replicate the problem. The truck shifted the best that it ever has, very smooth 1-2. Well, I took it to work this morning and the 1-2 shift is back to how it was before. I'm at a loss on what the issue is. Also, I am not getting any codes. Any ideas on where I should look next?