I installed a 6.0 and 4L80E combination in my 79, the engine runs great with no problems, but the trans does not seem to be controlled.

It starts off as it is slipping then shifts hard as if the torque converter is locking up, (2 speeds only).

I had the harness reworked by Dynatech and it is missing the Input shaft speed sensor, could this be a problem?

The engine and trans were working perfectly in the donor vehicle before I removed it.

Anybody have any ideas or suggestions. Worst case is change out the trans to a non PCM controlled trans, don't want to do that, but if I have to I will.