3rd dodge truck, lst one I have had any problems with. 1900 miles ck engine light. Problem with transmission. Replaced VTS Module. I pull 7500 lb G neck once or twice a month less than 50 miles each move. First pull at about 6000miles. Upon acceleration from stop I get a shudder in rear end. Stops at about 20 mph. Also strong acceleration 1st to 2nd, 2nd to 3rd, then and immediate shift and loss of accel. from 3100 rpms down to 2000 rpms. Finally all shift when towing(I tow in tow haul mode) are very harsh especially 1st to 2nd. Dealer has added additive to rear end and recalibrated VTS Module(19000 miles). Finally had to tow trailer to dealer for test drive. Initially they said yea something is wrong. Now telling me all is normal. this can not be normal. Any Suggestions. Note: Steering gear had to be replaced at 19000.
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2006 Mega Cab 4X4 auto, Stock,B&D Hitch, anti spin, 11.50 Rear Axle 30000 mi

 

I'm sure it's the propeller shaft U-joints shuddering when accelerating in the lower gears... is it more pronounced while loaded or unloaded?

What additive did the dealer put in the diff?