If your car shakes while accelerating check your motor mounts. Then check your transmission.
A vibration in the front end of a Volvo S60 while accelerating is due to imbalanced tires. Swap the tires until the right combination is achieved.
Have transmission fluid and filter changed. Checked Transmission mounts
Check the gearbox mounting.
Have the shop tha installed the motor mounts check and see if all mounts were replaced and if they are tight.
The transmission is usually pretty vibration free. Check the CV joints. Hopefully it is not the flywheel.
Could be a few things, I would check universal joints first. Also check driveshaft for damage.
It's possible that one or more of the motor mounts have loosened or broke. You'll need to get it up in the air to check. It's where the motor mounts to the frame.
The first thing I would check is for broken motor mounts. This causes the vibration around 40-45 mph. There is a service / recall bulletin about this at Kia.
It is possible, but there are so many parts that would have to be fabricated that is it likely more trouble than it is worth. The engine mounts, transmission mounts, drive shaft, shifter linkage and throttle linkage, would all be incompatible
If car stalls out when accelerating above 40 MPH, it can possibly be caused by fluid leaks. Another reason can be a defect at the transmission.
I drove a car with weak mounts it did not hurt the vehical over all. It just made the motor shake alittle it they brake I would fix them asap.