2002 Mazda Millenia Vibrations while driving

My car ran like a dream when I was told I needed new front axles, brake pads and rotors. I have taken my car to the same repair shop since I purchased the car in 2001. I had the repairs done and the next day driving down the highway, the steering wheel was shaking so bad I pulled off onto surface streets. I called and was told it may be out of balance to bring it back in the next morning. I did so, and the vibration was greatly reduced. Unfortunately their was another issue when accelerating at highway speed. When pressing the accelerator, the car would "groan" and you could feel it trying to accelerate but having a lot of trouble. I took it back in only to be told it "wasn't their problem", so I took it to another shop. Apparently when they changed the axles, some transmission fluid had leaked out and it was 3 quarts low. This was fixed and new axles were put on instead of the remanufactured ones that had been installed. There is now a vibration between 20 and 30 mph and above 60 mph. What could be causing this vibration? All of this started after the installation of the new axles, pads and rotors.