A. I'm hoping you now have the egr delete done?
B. There's many reputable rebuilders of injectors. My personal preference, and close to home, is Oregon Fuel Injection. Diesel injector pump, injectors, Powerstroke injectors, turbo and turbo parts for Ford Powerstroke Diesel pickups 6.9 L, 7.3 L, 6.0 L 6.4 L
C. Obviously stay with stock injectors if just replacing 3 of them. And that will commit you to staying with the stock ones.....I can't see tossing out 3 fairly new ones next year if you decide to try different injectors!
D. For what you are doing....(I assume the Hotshot thing)....when the bank account turns black, I'd invest heavily in getting the heads pulled and checked, studs installed, conversion to an ELC coolant, coolant filter and an oil bypass filter.
This is a LOT cheaper to do it yourself if you have the ability. The $10,000 you spent at the dealer was robbery. For far less than half that, you can do all the above in your own garage. If it was me, I'd swap out the 3 injectors right now. Then in about 8 months I'd pull the whole motor, do all the above as well as new rods and mains, seals, oil pump, water pump, the BPD oil cooler/filter kit eliminating the factory one, do the other injectors, all the updates such as turbo supply and drain, blue spring kit, new standpipes and dummy plugs,all hoses. Check the HPOP before digging in...if it's looking like the pressure is getting close to borderline, plan on doing that as well. Then you should be good for a zillion miles.
Note: If the aforementioned Ford dealerships blamed the dealerships for not fixing things correctly, I would use that report in writing to demand a refund. They do warranty the work they do to some extent.....I would push hard...very hard on that one.