[MarkMrtnFan2]

I've got a '99 f350 crewcab long bed with a 4" lift and have been experiencing an intermittant vibration in the drive train. It doesn't matter what speed, high or low, but it comes and goes when I hit a small bump. It will start with a bump and stop when I hit another one. So far I've rebuilt the rear end completely, had the driveshaft balanced and new ends put on, new Spicer u-joints, new carrier bearing, swapped transfer cases, eliminated the stock springs and add-a-leafs and had custom springs built to do away with the lift blocks, checked the tranny pressures and shift points ( it was rebuilt about 40,000 miles ago), checked the driveline angles, and replaced the rear yoke. Does anyone have any other ideas?? One thing I have found is that if it does start to vibrate, just switch to 4WD and it'll stop instantly even though the hubs are unlocked or I can leave the hubs locked in and in 2WD and it's ok...