Hi All,
Hoping some transmission Guys will step in . So a long time ago I purchased said 4L60e from what used to be Kiesler transmission . Terrible transaction that got ugly. When I got it in there was immediately a problem. Here’s the problem:
Put it in manual 1st . Floor it and it almost immediately shifts to 2nd or 3rd, it’s hard to tell . If you keep your foot in it and shift to 2nd manually it acts like it’s in neutral. If you don’t shift it manually and lift a bit it goes back into 1st .. Other than that it performs perfectly . Put it in 3rd or 4th floor and it shifts hard and on time . Have probably put 50k or more miles on it .

Have checked all electrical function at the plug on the trans while driving and all is correct .
Have removed the shift linkage and put the trans lever in first and same problem.

Talked to a local trans guy and he said replace the valve body .

What do you guys think ?

If I do go that route can I do it in the car ?
What do I get for a valve body ? I know 0 about transmissions .At the time Kiesler told me the valve body was specifically designed for their trans and they wouldn’t reveal what mods were done . I thought it was crap as they lied about a lot .

This is a mild street car 340

Thoughts?