Update
Got the new tires put on Saturday. Tire shop aired them up to 35 psi. When I questioned them on it they said that was the correct pressure regardless of whether it's a P tire or LT tire. Everything I've read says otherwise, that an LT tire requires more pressure to carry the same load compared to a P tire. Can't find a load chart, so I aired them up to 50 psi when I got home. I'll try that and see how it drives. Might be a little much for running empty.
Now the bad news...the noise I thought was road noise from the A/T tires is still there. It is definitely in the drivetrain somewhere, possibly wheel bearings or differential. In doing some research online I've found cases similar to mine with the Expeditions and F150. The hard part is going to be troubleshooting the exact cause. The noise sounds like it's coming from the front but it could be in back and just transmitting to the front through vibration. I don't know if I should have the dealership look at it or just start replacing parts. Replacement of a wheel bearing looks pretty easy. Anything more than that I don't care to get into. :(
