I have a 2007 Tundra SR5, 5.7 V-8 Crewmax (2WD), 18 inch OEM wheels
and i have the same problem going on newer paved roads at 65-70 mph. It only happens on a stretch of highway going west,... its the newer type of concrete paving (and not of the usual black tar) used on most highways. Although that cement paving is newly laid, fresh and smoothe, i've always experienced vibrations, (not as obvious though) on EVERY car i've driven in the past 15 years or so. A 99 Dodge Caravan, an old 87 Isuzu PUP, i've always felt some kind of difference between the tar pavings that merge into the cement type paving. I've concluded with rmjdrift that perhaps an empty bed will make it bounce even more. Also, my truck is still new and is still in the process of being broken in. I'm hoping that time and or experimenting driving with my bed loaded, will draw the same conclusion, That its more the ROAD and NOT the truck itself. I'll report back when I do. Hope this helps. PS - She's SMOOTHE on tar highways at 65-70 mph.