Vibration at 1400 rpm and worse at 2000 rpm
I new to this site and looking for some help. Just bought a 2012 F-250 XLT supercab long bed had 4500 miles on it when I bought it. I bought it about 2 months ago I drove it for a couple of weeks towed my camper put like 800 miles on it ran great. about a month ago I started to notice a vibration at around 1800-2000 rpm can feel it in every gear but is the worse in 6th at about 75 mph. took it to 2 ford dealers they say its normal. now im getting this same vibration at about 1400-1500 rpm its a very annoying vibration or humming it goes away if you not at any of the rpms listed. Is anyone else having this issue or is it really normal? any suggestions on where to go from here?