2000 Chevy Silverado vibrates between 50 and 65?

Could be many things:

Bad Inner or Outer Tie Rod Ends

Bad Pitman Arm 4WD

Bad rack and pinion 2WD

Unbalanced Tires

Flatsided Tires

Vehicle out of Alignment

And many more, regretfully to say go have it aligned and while they are aligning have them inspect the vehicle for problems.

2000 Chevy Silverado LT Ext Cab 4 dr 5.3L 4x4 Z71 who had the same problems but now has a new pitman arm, inner tie rod, new Cooper Discoverer ATR Tires, Lifetime Alignment.