vibration

Is it coming through the dashboard on the left side?

 

is the vibration coming from the drive tires? is it coming in /out at a certain speed? is i gear related?

 

I'd have a really close look at the rear engine mounts. Especially the left side. It's hard to see and harder to replace, but they are a common fail point on this chassis. Look for signs of the rubber de laminating from the steel. If you ever do a clutch, change them regardless.

 

OK, then it's probably not the engine mounts.

Thinking out loud here:

1) When is the last time the truck was greased? A dry driveline will give off vibrations.

2) tire PSI? Tires inflated higher than they need to be for the weight they're carrying, will cause vibrations/ rough ride. As will cheap tires.

3) #1 u joint- is it in good shape? A spun cap will cause vibration.

 

tire(s) out of round?

 

When my engine mount broke, the vibration only became obvious under heavy engine load.