I usually drive on interstates which the speedlimit is 70 miles per hour. I at first though it was a problem at speed at and above 70mph, then the other day I was feeling a little sporty and got up to 80...... maybe even 90

Well, the wobble went away. Only at 68-73mph does it occur.

Other symptom is its not constant. What would make a wheel wobble for 1 minute then go away for 1 minute?

I know the basics, drive shaft, wheel weights, etc. But what would make it wobble at a certain speed and on and off.

 

usually from my experiance with that has always been wheel out of balance...try rotating your tires and see if it goes away

 

In your other thread you say you need bushings. I'd replace all your suspension bushings then see how it is and go from there.

 

That is a tired truck, do a Tom mentions, after you have balanced and rotated the tires, then start looking at all your bushings, tie rod ends, wheel bearings and swivel pre-loads.

 

ditto what Mike said, if it's the confidence inspiring, beloved "death wobble", it's likely tie rod ends or swivel preload/bearings.

Just about all the other reasons are not so speed specific.

It's not the steering damper.

luck,greg