If they are aftermarket wheels/tires and it was done without changing the rear end gear then your truck is geared higher than your specs show it to be. If you came with a 3.55 you may well be into the 2s all of which will make it less powerful when towing. It won't make any difference in how WELL it tows but it WILL make a difference in the power you have. Change back to the OEM tire size listed on your DOT safety place in the door post and your trucks original specifications will be restored and you will have more towing power. It will NOT change your tow rating however. Tow ratings are a warranty issue and Ford is not likely to recognize any aftermarket changes you made in their warranty decisions.
Good luck / Skip
