this is my first post. I have a 2008 auto JKU. I have not been able to get a diagnosis of the following problem: the car vibrates when between 1,000 and 1,300 rpm and moderate to heavy load. In any gear. For example, of I'm going 50kms per hour and my rpm's are at about 1,200 (maybe in 4th gear, I don't know) and I start going up a hill, or want to accelerate, it starts to vibrate and vibration gets worse and worse if I keep the gas pedal there. If I let go of the gas pedal, it stops (I don,t have to let go completely). If I press harder on the gas pedal and force it to upshift (force it into higher revs), it stops. This can happen in any gear where I am at low rpms and never above 1,500 rpm.
It is not my tires, they are balanced; plus when It upshifts, the vibration goes away although the wheels are still turning at the same speed. I feel it is some part that is turning and is out of balance, and if that part spins fast the vibration goes away, but can't figure out which part. I thought it might be the drive shaft but it still has the balancing weights on it intact, so it can't be that. I never offroad (well...once years ago) so nothing should be bent. Any suggestions?