Transmission shudder?

Just move the gear selector into a lower gear position, the vehicle is hunting for the proper gear and being on a hill causes the vehicle to accelerate slower than on flat ground. 40 mph is when the transmission is trying to shift to the next gear, but since the vehicle is staying close to 40 on the grade it is downshifting after it up shifts. Changing the selected gear or turning off the OD should cure this problem under the conditions you have mentioned.

Check what fluid the shop used alot of them will use standard atf dex/merc you need atf Mercon 5 if not you will get a shudder. speaking from experience