Vibration at Deceleration

I used the transmission mount from my 904 with no bolt through the crossmember. The Duster just had a piece of 2x4 as a mount. I replaced it with the proper tranny mount. I measured my driveshaft, it was 3" too short. I took it to the shop this morning. They will also install new u-joints. The rear one was bad. So, I had the wrong tranny mount, a short driveshaft, and a bad u-joint. I'll put the driveshaft back in and go for a ride, see what happens.