Where else to check for vibration?

Long story short, I didn't get a chance to replace brake pads before they wore out so the pads and rotors were replaced at a shop. About a week later when I was driving on highway I noticed the car had pretty severe vibration in the steering wheel. I took it to Firestone since I have their lifetime balancing. The vibration in the steering wheel now is pretty much all gone, however there is noticeable vibration on the door, floor and seats when exceeding 50 Mph, I could even heard a faint cyclic noise. This vibration is most noticeable at 55 then becomes less again once the speed is over 60, I am going to take it back in for another balancing check, but could it be due to something else?

My vibration issues were:

Crappy tyres → replaced them (including balancing), vibration reduced.

Worn dampers → replaced with better condition 2nd hand ones, vibrations pretty much gone.

Only thing left for me to replace are the bushes.

But it could be things like driveshafts as well.

tires are the first bet. rotate them and see if the vibration goes away

Also check the edges of the tires for uneven wear.

Could one of the new rotors not be sitting flush on the hub?

Took it back for balancing again. The front tires were spot on but the rear ones were out. Got it fixed and that basically solve the problem. There maybe a tiny bit of vibration left but it doesn't bother me. I was surprised how much rear could affect the front end of the car.