I recently rebuilt my 93 4l60e from a gmc 1500 4x4 I have reverse, first which revs high then jumps to overdrive, if I unhook electrical connector it will go into limp mode and third gear only, there are no codes showing, any help will be soooooo helpful and appreciated.

 

I have a similar issue. Put an LS1/4L60e from a 2000 Camaro into my 77 C3. Have not been able to get the transmission to shift past 1st. I have Park, Reverse, N, D (But only 1st). I have limp mode if i pull the plug.

My pressure is also high in park, about 200psi.

VSS puts out volts when I turn the wheels, TPS has 5V, no codes.

Either my harness is not doing the job or i think its not grounded well enough.

Has anyone had an issue with a bad ground really affecting shift performance?

 

I would suggest first replacing the shift solenoid; Solenoid A stuck in the ON position would give you only 1st and 4th gear.
I realize that is not consistent with limp mode; assuming you are absolutely sure limp mode is giving you 3rd gear and not 4th.
Note: a shift solenoid can "stick" in the on or off position without throwing a code.

If its not Solenoid A, it could be short in the wiring harness (internal or external) or a faulty PCM.

Mark: I answered in your thread; lets continue your discussion there. I don't think they are related.

 

ok thank you I will check solenoid A an post results