Been going through this same problem everything double checked..Found my driveshaft to be .030 out of true. Having it straightened as we speak...hopefully that fixes the vibration...if not ???????
If you happen to find a good one to install, suggest you pull the torque converter and change the front seal..Lot of work to have to pull later just for a seal
77 gmc had slow power windows.. Replaced worn out regulators and that totaly solved my problems. The old ones were not only worn but the rollers were trash. Also you can run a direct 12 V from the battery to the motor and see if you have a wiring problem or switch problem. Good luck
Upgrading to 134a and want to install a new style compressor. Any suggestions what vehicle will interchange with my 77 square. Small block with compressor on drivers side. I would like to keep the original dual hose mount which come out the back of the original.. I know the sandens and others...