Originally Posted by osiris419
Thanks. I'm going to get it rebuilt. My old college professor is teaching an automatic transmission class with his auto tech students and is going to take my truck as a training aide. They are going to go through it and troubleshoot it and overhaul it. All I have to pay for is parts.
This is not a transmission for children to learn on, this thing is wickedly complex, it is basically a computer directed, electrically managed, hydraulically controlled version of the mechanically managed, hydraulically controlled 700R4. Basically, the 4L60E includes the nightmare of the 700R4 with all that electronic/electrical stuff on top of it. Part of the controls both electric and hydro-mechanical are inside, with electronic to electrical controls strapped on the side. The functional schematics of this thing show all that stuff as inside a box called a valve body, the average guy doesn't even know that part of the "Valve Body" is on the outside. It does not take kindly to people who are ignorant of it. This is a good way to end up owning a piece of expensive junk.
At 200,000 miles it's given it's all, that's well over the design life expectancy. Franky, since you don't know how a junk yard tranny has been treated, and if it has many miles on it the probability of it, also, needing a rebuild is real high. I'd suggest you either just scrap the truck, or take it to a shop that knows what they're doing to have it rebuilt. You can get a rebuilt stock 4L60E for around a grand and a race ready unit 1800 bucks (plus installation), this is a lot safer than spending 500 bucks at the wrecking yard for what more likely than not is a pig-in-a-poke.
I'd hazard a guess that on top of the general wear, the tranny is loosing line pressure as it warms up. On the surface without digging deeply into it some common causes of this are a failing Electronic Pressure Control (EPC) motor or its filter, and/or leaky internal seals (many of these are plastic, some require complete disassembly to get at and that's not cheap). So the answer could be simple and not to expensive, too really expensive along with worn clutch packs, leaking servos , swallowed check valves, it has a nasty habit of sucking some of these right thru the hydraulic valve assembly's divider plate.
There are a lot of houses around the country that rebuild these from mild to wild, I get on Google and do some shopping, I think in long run it will prove to be cheaper than attempts at a bargain repair.