Wow, for a second hand rig that lokks amazingly clean! It does not look like it has been used very much at all, and it was well taken care of.
First off though, I would replace the air filter with a better two stage filter, something like a motor saver. Second, make sure it has a fuel filter, if not add one. Then just give it a good once over, check all the screws make sure they are tight. Especially the grub screws in the drive cups, they are notorious on that rig for coming out and then the driveshaft just spins while the truck goes nowhere.