Using a floor jack, lift a front wheel off the ground a couple inches by placing the jack under the lower control arm as close to the wheel as possible without touching it. This will take the weight off of the ball joints. Using a long pry bar place the bar under the wheel and try to lift the wheel. If the joints are worn you will notice movement or play as you lift the wheel up and down. Have someone look at the joints while you do this to determine if the play is coming from an upper or lower or both ball joints or the upper control arm bushings. Be sure the wheel bearings are properly adjusted (2 wheel drive) before you do this procedure.
Check for a loose connection Check for a loose fuse in the fuse box Check for an open wire in the brake light circuit
A chevy 3500 truck is not front wheel drive, so it does not have CV joints.
Some could be's, Bad u-joints in driveshaft, Bad transmission mount. Transmission cross member loose.
what year and do you have a 4l60e trans if so the trans might be going but firs check the u joints check all them the 4l60e is natoris for having the trans go
replace the worn parts.
Check your ball joints and your spring hangers
I'd focus attention on the U joints or if it's a 2 piece drive shaft, check the center "carrier bearing".
try tread lock.
Check out this site, http://www.nadaguides.com/
Check out LMC Truck catalog.
I think it would work but you might want to check before you try
Assuming we are talking about the rear oil seal on that transmission, if it has been replaced and it still leaks, check the condition of the universal joints in the driveshaft.