I just installed my lift SAW C/O and Alcan 8 leaf springs..When I give it gas the transmission seems to stay in the gear a lil longer before changing..It changes smooth..And when foot is on the gas pedal it vibrates and you can hear it also..When you let off it stops and you don't hear it anymore..The best way to describe the vibration it feels like a foot massagger on low..I did a search with no results...

 

Check your rear driveshaft pinion angle:
- http://www.4crawler.com/4x4/ForSale/Shims.shtml#FAQ1

That could be off with the lift springs in back, especially if you have a 2-piece driveshaft and did not install correcting shims with the lift springs.

 

Definitly check your drive shaft bolts. A friend of mine lifted his f**d exploder, and took the drive shaft off. Apparently he was supposed to use lock tite, and when we were driving around, the exploder had a bad vibration, and then the driveshaft just fell off(well, the front of it anyway)

 

I did not shim it..I did alot of reading and never where I needed to..I will check into them and get them installed...Please keep coming with other things to look at..

 

I still need to adjust the front end and crank down my SAW about another 1" to level te truck after all said and done I got just over 2" of lift and agreat ride...

 

I got to drive it yesterday on a long run from 30-60mph the vibration/noise you can really tell but on higher speeds it gets less noticable but still there..

 

Maybe u joints??

 

I did a 1.5" spacer lift on my front end and got noticeable vibrations. A 1" diff drop helped things but didn't entirely eliminate the vibs. If the SAWs are adjustable, try lowering them and see if that improves things.

 

it only does it when there is a load on the engine..When I let off the gas it stops and when I apply the pedal again it starts back up..I don't think it's the CV..I am thinking driveshift or u joints..But the sound is coming from the center of the truck under the dash..