I just posted on the similar "shimmy" thread.
- Not wheels and tires (at least on mine, I had them swap my 2012 OEM 20" wheels on this truck when I traded for this 2013 - never any vibration at all in that truck, this 2013 vibrates 50-70mph with either set exactly the same.). The wheels on this truck also 20's, just liked my 2012's more.
What I want to know is what is the common denominator component-wise for this issue?
My 2013 truck is a 4x4 CC 5.7 with 3.92 gears and 6 speed.
The 2012 I traded in for it (and swapped the wheels) was a CC 4x2 Express that I never had one issue with in 3 years since new. Drove smooth and straight.