Q: Car vibrates/shakes at 55 mph

A couple of months ago, my SUV had a flat tire. It had been going flat gradually, so I just added air, but then one morning - completely flat. I added some fix-a-flat and took the tire to have it patched, but they couldn’t find the hole. It drove for about a week, just fine, but continued to slowly lose air. I bought another product and this one was supposed to be more permanent. We had to take out the valve stem in order to completed deflate it, then pump in this product, replace the valve, and then add air.

The next day, while driving around 60-65 mph, the car started shaking and it seemed to move across the car - first on the driver’s side and then the vibration would move across to the passenger side. So, I had the tire replaced, thinking it was beyond repair. But… that didn’t fix the problem. Two days later, the tires were rotated and balanced… no difference in the problem. I did the alignment self-test where you let go of the steering wheel to see if it pulls to the side or stays straight. I didn’t get an alignment.

Two weeks ago, I had another flat tire - just completely blew out. Thought that was the problem - no it wasn’t (it was actually my replacement tire). So… the past few days the vibration/shaking has gotten worse. It starts around 55 mph, sometimes lower and gets significantly worse as I increase speed. What is causing this and how do I find help to fix this?