Bad need of some 4l60e HELP !
One thing you mentioned that threw up a red flag is that you used degreaser on the internal components. This could have caused rust that has resulted in seal failure. Pull the trans and watch the videos as you disassemble and reassemble the transmission per his guidance.
To the OP on replacing the 3rd accumulator checkball capsule, it's a 3/8 by 16 bolt, 4 inches long should do it if you decide to replace it. An AC Delco one is around $8-10.
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I see no problem using a new-style steel 3-4 piston with old-style Forward and Overrun pistons. Why do you ask?
Since you have looked at Cory's thread, did you use the new style spring cage? I don't think you could even assemble with the new-style piston and the old-style loose springs.
Also, what city are you in?
Google the part number and an Amazon link should show up in the results.
However 80 in Reverse is extremely low - the Reverse fluid circuit pushes on the Boost valve to raise the pressure. I typically see 175 psi. (However I have very little experience with other people's transmissions, just the ones I build.)
150 when you touch the gas isn't bad, just a bit low.
I suggest getting the Sonnax 4L60E-LB1 boost valve ($30); it is trivial to install after dropping the pan. The larger boost valve will raise pressure and its o-rings will prevent leaks. With the pan off, I would also replace the Pressure Control Solenoid (PCS) just to be sure.
Another useful test would be remove the trans connector, if you can reach it. This will cause the trans to go into limp mode (3rd gear only) but also raises the line pressure to max.
With the Sonnax boost valve and everything working properly the max pressure will be closer to 225.








