Toyota - Tundra :: Sneaky Intermittent Vibration Even At Lower Speeds

When I bought my 2007 tundra used a year ago, it has always had a vibration that affected the whole car (not steering-wheel specific), and was worst at 60-65mph, but a hint was there even at lower speeds. It was annoying, but bearable, for example if you look at the passenger seat at these speeds, you can see it wiggle back and forth about 1/2". It seemed highway speeds were where it hit a resonant frequency.

In the past month, things have gotten much worse and when the truck has been sitting for a few days, if I quickly leave the house and hop on the freeway (only about 1/2 mile away, I get a vicious vibration mostly in the steering wheel and less so in the rest of the cab. The wheel wiggles about an inch and a half back and forth at highway speeds and letting off the gas, braking, accelerating doesn't make much of difference, just speeds up or slows down the vibration frequency.

The wild thing is that it gets much better after about 2-3 miles. No longer really shaking, just a mild vibration like it has always had. If the truck is warm and I hop back on the freeway a few hours later, no vibration, just when leaving the house in the morning.