Shake, Rattle, and Roll

[GGott]

Hi Fellas, My W250 has an ongoing vibration (shake) problem. I'm running out of ideas, hope you can help. The shake starts around 45mph and continues upward. Happens whether in 4th, 5th, under throttle or off, and in nuetral coasting downhill. Doesn't seem to be rpm specific. Starting at the front: Tires are 1yr old, on straight rims, and even tire pressures. Brakes allround are good-new rotors, calipers don't hang up, good condition. Wheel bearings to spec. Upper kingpins new, lowers tight and good. All steering linkage tight and good, steering box tight to an uncracked frame, Borgeson. New motor-transmisson mounts, tight to spec. Exhaust tight and properly hung. Cross members (rivet and bolt) tight. Drive shaft, straight and runout in spec. I have one leaf added to re-arced front and rear springs to bring it to aprox. stock height, the rear spring hangers show little end play. Ran the truck on a hoist to 40mph and no apparent wobble from rear axles. Any thoughts and ideas would be greatly appreciated.