Re: Vibration - '04 F350 4x4 Crew
I'd say either a wheel bearing, or an out of balance drive-shaft would cause an increase in vibration as speed continues, even coasting with the transmission in neutral. Chances are that the truck was previously a tow vehicle, as it's a F350 4x4. If the wheel bearings and shafts are fine, you either have an out of square frame (unlikely, or they wouldn't have been able to sell it to you, but you never know), or something in a differential or transfer case is causing the vibration.
To rule out some of the items, find a road that is NOT busy and make sure it goes downhill. Bring the truck to a stop, put the transmission in neutral and then the transfer case in neutral and coast down the hill with the engine running. If the vibration goes away then it's obviously drive-train related. Then be sure to stop completely and reengage the transfer case and transmission.
'00 Durango R/T 360ci 290hp (modded); 138,500m
'06 Pontiac G6 GT 3.5L 220hp; 44,000m
'12 Chrysler 200 Limited 3.6L 283hp; 13,000m
'99 Taurus 3.0L 2V Vulcan 145hp; 154,300m - Traded
Amsoil in all vehicles!