I own a 1998 F-150 s/c 4x4 4.6 L auto Trans. My problem is that during acceleration the 4x4 shifter shakes terible under load. As soon as i let off the gas the shaking stops i have had the U-joints changed the drive shaft balanced Trany looks good when i pulled the pan nice and clean but no one not even the dealer can figure this one out. I hope that someone out there has had the same problem and can give me some suggestions on possible solutions. thanks.