4L60E 4L70E Limp issue

[smokymtn65]

Working on an 07 4L70E that went in limp mode, codes were C0379, P0756. At this point the original builder is working on it. So basically for 100miles it works fine then suddenly goes in limp at tries to pull away in 3rd. Warm or cold doesn't change it. So far TCM, separator plate, valve body, internal wire harness, all internal electronics have been changed. Ignition switch has been changed. External wire harness inspected, for fray and damage. Fuse box pulled and inspected underneath. In initial inspection i found a piece of what looked like gasket material is 2-3 shift valve but rear valve i dont know proper name it wouldn't move freely. But since them the whole valve body has been swapped. Builders last resort was i will just build a new one. I was hoping someone had an idea of something we are missing.
@THEFERMANATOR

 

[dbrannon79]

could this be something in the PCM programming? I recall @Rockabillyrat talking about this somewhere.

 

[Rockabillyrat]

There was a updated TCM calibration for that code. But if you had the TCM replaced then the latest calibration should have be flashed into it.

You need to check line pressure and confrim its in spec.

Other possible causes for that trouble code are the control solenoid assembly, lower control valve body, 1-2-3-4 and 3-5-R clutch housing assembly, pump cover assembly, low clutch sprag assembly, pump seal.