Bad Tire???

[Zilverado]

Man, it seems like forever since I've been around - just all together too busy I guess.

So I had the truck out on the highway today, and it seemed as if the pulling to right (which I've had for a while) was getting worse. When I got home I jacked up the front end and took a look around, but couldn't spot anything obvious. So I swapped the right and left front wheels. Took 'er for a test drive, and low and behold, the pull was mostly gone. Now there was just a bad shaking in the steering wheel - well, actually the whole truck - at certain speeds.

So after all this, I'm assuming the culprit is a bad tire. I can't really see any defect, but I haven't taken the time to look too close. Does anyone out there have any comment? With the fact that the initial pulling seemed to slowly get worse, a deteriorating tire does seem to make sense, but...

Any thoughts?