2003 Alero-Shuddering problem

I have been recently noticing for a couple weeks now that when I get up past 75mph, I have a shuddering problem. This also seems to happen if I brake from speeds higer than 55mph. Does anyone have a clue what could be causing this?

Thank you

Tire balance at about 72 can really mess up the ride. In my exp. you can be fine up till about 68 - 72 an then instant annoyance. The pads can also cause imbalance. Anything seems to be a problem at that speed. It is a sweet spot for shaking.

If your tires are imbalanced, you'd notice it around 40-50 mph (once you reach highway speeds mostly). Brake pads won't cause imbalance in the tire because they're not rotating with the tire, they sit stationary on both sides of the rotor. Is the shuddering coming from the suspension or engine?