Like the other have said, be sure to know how they are making the payments the same.
Other than the 4wd going out, it doesn't sound like you have had major problems with the truck, some of those things can be expected on a 7 year old truck.
How many miles does your current truck have and how many will the newer model have? that would be one of my major concerns....
In any case, it sounds like this dealer is really taking care of you.