I've got the 20" wheels on my F150 and the tires are the Bridgestone Dueler, but the 'hwy' version.... Nice tire, but it's gonna suck in the snow! ;)
Towing my #5000 TT with the tires pumped up to the max 44 psi feels just like it did with my LT C 16" tires I had on my old F150..
I don't have any mushy or soft feel with the P tires at all.. Probably due to the lower "55" series profile my tires have. (P275/55/20).
I'm probably going to see how these do in the winter time and decide from there... I'll probably go with a P or XL tire regardless, just in an "A/T" tread design, as they have gobs of choices for those in my size...
Good luck!
Mitch