Car shakes when accelerating over 55 MPH but doesn't shake when foot taken off gas

It sounds like the motor and/or transmission mounts are bad. You can check the engine mounts by;
putting the car's parking brake on
opening hood and get a line of site on engine
start car end rev engine in neutral and see how much it moves and what kind of noises it makes when it comes to rest
Put the car in gear and give it just enough gas to make it start to lunge which will load the motor and make it move.
If it moved more than an inch or two the mounts or a mount is failing. When one mount fails it wuickly makes the other mounts faill as the load of the eninge is distributed to the mounts still able to hold a load. So, if the motor made a noise when it came to rest and moved excessively the mounts need to be replaced as a group. That is all engine mounts and tranmission mount all replaced at the same time.
The only other ideas I have are that the alignment is bad on the car and the, "TotalToe" is not adjusted correctly.
You may have bad axles or wheel bearings.
But, you must eliminate via process and with your mileage these parts are dure for replacement.

That is too bad that that happened. You have to be carefuel with CV axles or they will slip out of the bearing carrier. Although I cannot see how the tech did not motice that the problem had occurred as it is pretty obvious when it happens. At least you got it fixed.
I am glad it all got sorted out.
It is always good to hear that things went well and got taken care of.
Come back anytime you need anything as we are always here to help.
Thanks
Dr. C