Mike,
Stan is on the right track. It sounds exactly like the problem my neighbor was having with his pickup. The rear u-joint was dried out and it locked up on one set of the bearings. I pulled it out and got him fixed up within 2 hours. He said the truck drives like a new one now.
The problem usually occurs with the back u-joint drying out. The vibration will happen under power and will follow the driveline all the back up to the engine. That's why you can feel it in the steering. If you listen, you may hear a small chirping as you are giving it gas when you start out.
Give me a call sometime and maybe I can give you a better deal than the local shops.
Later,
Tim
PS. Autozone has u-joints for that car that run between $9.99 and $15.00