I’d say start easy….how’s the fluid level? You checked while running in neutral right?

and have you ever adjusted the tv cable?

 

The first startup it started with no issue, we had to remove the inspection plate on the bottom of the bell housing because the flex plate was hitting it every full rotation. Fluid was filled all the way up with truck running in neutral then shifted through each gear to fill each slot to its allotted amount. It shows the fluid is now at max level when checking it and we got it to engage in drive and move forward about 10 ft but it seemed like it was in 3-4th gear with the lack of power,