Automatic Transmission - Problem What could it be.. Help me out advice?

Well i just got a new built tranny... The tranny works great at full throttle and normal too.. but when it goes to over drive at 45-55 .. i slightly accelerate a little fast but not full throttle and it makes a shudder noise and even my dash shakes violently then goes back to normal.. it feels like it goes back to 3rd then overdrive and in between that action it does that wierd vibration shudder noise that shakes the truck... could motor mounts cause that? or transmission mount.. or could it be a loose torque converter or that its going bad.. or maybe the bolts are just loose?

also feels like it holds the gear a little then lets it go... could it be the TQ that the sprag or how you call that little teeth fkn up?? help would be gladly thanked :)

anyone ?

ttt???