Does anyone here know of a programmer that one can use to correct the
speedo for tire size and gear ratio changes? I have a 285/70-17 tire and would also like to
install 4.56 gears.

 

As I recall, you can go to the stealership and they can reprogram it (call ahead for a price check )
I'm not too familiar with the programmers that are out there (I'm sure someone thats "in the know" will chime in) but, usually if they can change speedo calibrations, it will say so, or an email to the maker will clear things up.

 

Superlift Truspeed

It doesn't show the Gen II Durangos on the application guide, so I'd contact Superlift to see if there has been an update.