Wow, I stand corrected. It sure did sound like an alignment problem though.

 

I have the Toyo Proxes S/T. Thier directional so it make it very difficult to keep from cupping since the only get rotated one way. The vibration issue was fought for about 6 months and they said it was a few things like the smaller side wall, stiffer truck suspension, and stiffer steering. Basically they said it was the bumps in the road I was feeling. You can feel it most at freeway speeds. I got two new front tires out of that issue, and I didn't hesitate to go get another free tire when one got a slash that wasn't repairable.

Ford told me that it is because of these tires. They need to be at lower psi, and they are going to grab every crab in the road and follow it, and they do, but not as bad with the lower pressure. At 38psi the tires were riding on the middle. Now they are about 30-32 and it seems to be working.

I now for sure my next set of tires it going to be something more for trucks and non-directional. Like a good all season, but I am still keeping my 20" rims for sure.

 

are they P or LT rated? I'd see if they'll slap a set of normal 17" or 18" on their and do a road test. To see if the vibration is still present.

your 20" rims will cause a rougher ride, but your dealer is full of B.S. to say that a vibration while driving is normal. A vibration at highway speeds leads me to think of bad rims or improperly balanced tires.

My Mustang has 4 directional tires with 1 1/2" - 2" of sidewall max. I have alot of bumpsteer when using the brakes, but otherwise no vibration from the road (oh yeah, it's been lowered 1 1/2 inches also). The Mustang rides alot harsher than the truck.

This is one of those conundrums that I'd like to see the resolution for. As I'm sure you are. If I lift my truck, I'm planning on running 35"-37" tires with 20" rims to minimize the sidewall height. I don't want to have vibration issues if the 20" are prone to it.

 

I also have bump steer when using the brakes but usually the lower the speed the worse it is. The vibration isn't from the truck. If I really pay attention to the road and every little minute crack or difference in the road I can feel in the steering wheel. The vibration isn't the same all the time it changes with surfaces, and different roads. I did a little test earlier today, and when I grag the steering wheel and just barely bump the tire I can feel it in the steering wheel.I looked at the tire for a second earlier, and I it said something like P and ST. I don't know if that is the rating you are looking for.The tires and wheels have already been road forced and perfectly balanced many times just to make sure that the vibration issue was the road and not anything with the truck.
I think that if you go with a 35 or 37 your tires probably won't be proxes S/T's, and you will have a good sized side wall with 20" rims.

 

I had the same problem with my 05. I put a leveling kit on over a year ago and had the truck aligned then but it still pulled to the right. I just now brought it to Ford because the right side front tire was wearing on the outside much faster than the other. Its fixed now and it drives SO much better. The alignment was still out after I had it checked at NTB.