I just did a fuel injector flush using the Ford Motorcraft fuel injection cleaner. That stuff is nasty. Its not the kind of stuff you can put into your tank as it eats hoses etc.
To use the ford stuff you have a funky can with a place for an air hose on one end (to pressureize it) and a hose that goes into your fpr.
You then disable the fuel pump (I used the ineria switch to do that) and block off the return fuel line (you don't want this stuff going into your tank)..
You then put a little gas into the can and then pour the bottle of cleaner into it. Close the lid, pressurize the can to about 35psi and then start/run the truck off that.
The jobber cost for the cleaner stuff was $20/bottle and I used to bottles. The stuff really worked well, much better than any drop in the tank bottle did.
I'm not sure if I'd do it at only 77k miles (I did mine at just under 300k) but I would say every 100k or so miles it "may" be worth it.
BTW.. the procedure for yours may be slightly different at you don't have a return line for your fuel.. (I think the regulator is on the pump on your truck.
~Mark