OT 4L60E

This truck has been having issues for a while and there have been many little problems but I'll ask about the biggest problem. The truck shifts as soon as possible. The shifts are very clunkish. The rpm needle drops like lead and it's a very rough shift. Not crisp, but rough. When it was working it would shift into 4th-lockup at about 40 mph and only when it was warm. Now it shifts at as low as 30mph and locks up even if it hasn't warmed up. Even at -20C it locks up. It locks up in gear and don't want to unlock in R, 2, 3, and 4 th. Not sure if it would lockup in 1st because the truck is never in 1st. To stop it either pulls the rpm's way down until it nearly stalls and finally unlocks or it will stall. pop it in neutral and it will stop no problem. Other rare times you'll try to accelerate and it don't want to move. rpms won't increase and it kind of shudders which makes me think it is locked in high gear because when you put it in N it has no problem revving. It pushed me in the ditch once now so it's off the road till it's fixed. I'm not sure if lockup is the right word because I thought I read somewhere that they can't lockup in R,1 and 2.

It was too painful to read that whole post, but you need to look beyond the tranny for the full scope of your problems as the shift points and shift firmness are all controlled by the 'puter.

I know the post is sorta long but I don't really want to leave half the info out. I hadn't really ruled anything out but I find it odd that once the trans is in N that the engine revs fine. Everything works together does it not? Half the computer does't work on the trans and the other half on the engine so why does puting it in neutral help it rev. Can just certain portions of a computer go bad?

First things first,what year and what trouble codes were pulled from PCM?

Some may have had a sticking lockup valve. About a $300-400 fix at a shop if you can get a shop to do it. And if it hasn't broken internal parts from locking up so hard.

It would throw the lockup code.

Is the trouple light on? Sounds like a failing input sensor that is sending the wrong data to the computer.
Or a failing transmission the computer is trying to compensate for.
Time to read some codes.