Check simple things first:
Oil level in transmission is correct,,,parking brake applied, engine running, trans in Drive (have someone hold their foot on the brake) and check oil level
Throttle valve cable is correctly adjusted....700R4 trans MUST have the TV cable connected and correctly adjusted....
All engine and trans mounts are intact...
Did you check / change the trans oil filter before installing the trans?
Are the trans cooler lines in place, not blocked off....
