Short Story:
Wife calls from the mall says the Disco sounds and feels like a tire is almost flat but she checked and all are good. I drive up to see what the issue is, and let me list the symptoms and my thoughts, as I have not been able to get here up on a lift yet.

a. yes it does feel like a low tire or a badly cupped tire, all tires have good pressure and are not cupped.

b. crawled under to have a look tried to rattle front and rear drive shafts both are solid

c. did a test drive around the parking lot and to start there was a kind of rattle and vibration, which the rattle stopped and the and the was not as severe.

First I told my wife that I am not and would not be mad just to tell me what she had been doing right before the vibrations started. All she did was park the disco and went shopping and when she got back she started her up and released the parking brake, put her drive and the rest is history.

Yesterday I was able to reproduce the rattle noise and heavy vibes by engaging the parking brake and driving. The vibe is at its worse between 15-20 and 40-45, it also intensifies when releasing the gas pedal, I suspect the parking brake as the issue, with either a shoe that has come apart or something just broke.

Does anyone have any thoughts on this?

 

You can drop your rear driveshaft and pull the shoe for the parking brake off. Be sure to chock the wheels, or it can roll on you with the rear shaft removed. Weird that it would have these symptoms, but it is a place to start.

 

That is where I think I will start, should be able to get to this Tuesday night, can you think of anything else that would cause this???

 

I think it is your front driveshaft getting ready to let go.
I would NOT drive this truck another inch.
Have it towed and either rebuild the front driveshaft yourself or have it done.
If it lets loose you will be buying a new transmission.
Remember that both driveshafts are connected so setting the parking brake will also affect the front shaft.