Voyager tranny rumbles in reverse

Newbie Here...

I just had my cv and my motor mounts replaced on a 96 Grand Voyager and that solved an aggressive shimmy at 40-50 mph.

Now I've got a shuddering vibration when I put the car into reverse. It goes away if I drive in reverse for a few seconds. Any clues? Could the bad CV have been masking the vibration? Could this be a problem with an after-market cv?

My wife thinks I shouldn't drive it.

Unfortunately, I don't entirely trust my mechanic at Sears to give me a straight answer. I assume something is wrong with the cv install?

Thanks!

Are you sure it's not your transmission? How may miles do you have? What year? What transmission? Why did you have the CV replaced? Did you replace just the CV or the entire axle?