99 dodge ram 2500, 360 magnum, 5 speed manual, standard cab, long bed, ex forestry truck, rear suspention of a tank, will beat you to death empty, vibration problem, u can start to notice it about 60-65, gets worse up to 70, then kinda levels off, sometimes get up to speed in forth no vibration, shift to 5th and starts, once it starts wont stop, have pulled over and taken off again and will vibrate in 4th after that, vibrates in neutral, cluthched in gear, had trans rebuilt, bad syncro, didn't help, on lift with tires off ground wont vibrate, drive shaft looks straight, single piece, cat and front cab mounts were cracked when bought it, replaced cat with universal from advanced, went on three hour trip, 1.5 hrs into trip cat snaped at factory weld, exhaust support ripped off pipe at transfer case, which was the factory location for support, by the time I got home a week latter one of the down pipes had also broken at the cat, replaced it again, it has broken at the back part of cat again, I suspect that this vibration is also responsible for broken cab mounts, also put brand new steel rims and tires on truck, absolutley no difference,