Re: transmission solenoid pack problems
Did you fill the transmission already and it still goes into limp mode?
The P0750 code was indeed pointing towards the solenoid block, since this code is for the L/R solenoid (low/reverse). The P1786 is the pressure switch for the L/R clutch, which probably was caused by the failing L/R solenoid.
The P1768 is a " Transmission control relay off" code. This is a normal code when the TCM switches the transmission in limp mode. The TCM just removes the power to the relay.
If you still have the problem, then you should start with checking the fault codes again, before changing any more parts.