Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
A scan of the system is very important to help you narrow down the fault.The failure you describe sounds like a crankshaft error or a mass air flow sensor failure.The transmission is electronic controlled & the ECM determines when it shifts from input sensors.
Take a look at the wiring to the ALDL.Check these circuits.
Right lower pin #16 should have 12 volts
Left lower #9 data line to ECM (tan wire)
upper left second pin #2 purple wire class 2 data to ECM
Upper middle pin #4 from left should be ground
upper next one #5 ECM ground
Upper far right pin # XXXXX(top right corner) keyless entry reciever module(blk/white)