BOB, MY 94 3/4 TON 4X4, HAS DEVELOPED AN EXCESSIVE VIBRATION. IT GETS WORSE IN REVERSE, AND WHEN STOPPED IN DRIVE WHEN I APPLY THE BRAKE. I'VE CHECKED ALL FLUIDS, NO PROBLEMS THERE.....BUT WHERE?

 

Sounds like your idle speed is low.

 

How Would I Check That? Do You Think It Has Anything (the Vibrating) To Do With My Driveshaft? Thanks

 

You have a '93, so a scan tool can be used to read the RPM off the computer. You said that the truck vibrates worst when idling in Drive, I can't see how the driveshaft would have anything to do with that.

Also check the engine and trans mounts.