I have thrown parts at this trans and it is still doing the same exact thing. I got a line pressure gauge and tested it. At idle in P, N or D it would be at 40 psi, once I gave it a little throttle it would jump up to 90. When I drove it, it would get up to 130 +- 20. Reverse in idle was 60, but once I gave a little throttle it would jump up to 100+. Hard to get good reverse pulls monitoring the gauge, but it seemed reverse would go above 150 psi pretty easily while driving it.
So I figured I would replace the valve body with a remanufactured one using the transgo upgrades. She still does the exact same thing. Holds first until about 4k rpm and shifts hard. All other gears shift fine, maybe a little harsh, but all at the right range. Reverse takes a couple of seconds to engage. Absolutely no slipping at all.
Also, last night when I got home from a 30 mile drive I pulled forward to parallel park, when I put it in reverse, she stalled. I started her back up and went backwards and parked. She spewed tranny fluid out of the dipstick and made a mess. I have checked the fluid when hot and had her exactly where it should be.
Next I have ordered the speed input sensor. The only other thing I can think of is internal issues like the pump, which I am hoping to avoid. I really don't want to rebuild this trans, but I have rebuilt a couple of 4l60e's.
Any help would be appreciated.