For all those who have installed one, its larger than stock and firmer. My question is its causing a thunkiing sound upon acceleration. Is it because its firmer and larger? Drivetrain out of alignment?

 

The 1LE tranny mounts aren't larger than stock. It may seem that way cause your stock one sagged. Are you sure you bolted all of the bolts back up. Usually the clunking is caused by a lose or torn mount.

During one tranny mount swap I managed to strip the threads in the tranny and it was causing the clunking again.