Off the top of my head ….
You could try putting the vehicle up on jack stands,
Start the engine and put it in gear and see if the engine is being loaded down by the transmission.
Only problem maybe is, the weight of the vehicle may be contributing to the issue and without it you may not see a problem.
You could also drain the transmission fluid and see if there is any excessive metal floating around in the fluid
Also might consider dropping the transmission pan and look for any debris.