@ the dealer now... are they retarded?

my truck was at grappone earlier this week because of the blower and they say that there is nothing wrong with it and the mechanic looks at it and hears nothing, also the cracking noise I get it also going over bumps just doing 30 mph I have no idea what it is, and of course they couldnt hear it at the dealer also

 

If it is the rear driveshaft, then I'd try a carrier bearing drop first. If that doesn't fix it and the vibration is still there the next option is to install axle shims. Most go with 2.5-3 degree shims. Most of the time you run one or the other, not both at the same time.

It's easier and takes a lot less hours to change the front differential than replace bearings. The cost is around $2,000 if I remember correctly. You can search for "Front Diff Problem" and read about it.