I recently put on a set of 285/75r16 tires on my truck after getting rid of the 155/65r16s that were on there and the speedo is off. What do I need to do to correct that?
Thanks

 

New speedometer gear!

 

Where do I get one and how hard would it be to install?

 

Put "speedometer correction" into the search feature here and you'll find info on what new VSS (Vehicle Speed Sensor) gear you'll need, where it's located and how to change it. I'll be changing tire sizes on my truck in a few weeks and I'll be doing the same thing.
From what I understand, you should be able to get a new VSS gear from your Ford dealer.

Kevin