Another Vibration question

I have a 2001 Silverado Extra Cab 1500 with a 5.3 liter and is lowered by at least 4 inches. While crusing on the highway a vibration starts to occur at around 75MPH. Also, when attempting a hard excelleration from a dead stop i get the same vibration until i let up off the gas then it stops. The dealer i bought the car from had the drive train checked out and said the u-joints were fine. Anyone know what this vibration could be? I have the GT4 and GTU options for the rear end.

check the slipjoint in the driveshaft. theres been a few problems with these they require periodic greasing

check the slipjoint in the driveshaft. theres been a few problems with these they require periodic greasing

Thanks, does lowering the truck have that much effect on the driveline?

Thanks

This is rare, but a cracked flywheel may be the cause. Try pressing the throttle while holding you foot on the brakes. If it happens under this condition, it may be worth a look.

thanks, that would explain alot because the vibration is only there under power. A drive line/ rear end problem would not go away under no power. Since i bought the vehicle used a week ago it is still under warrenty.