Lots of conclusions being jumped to. Here is my C-9 experience. I can turn a wrench but knew very little about diesels untill my adventure in expediting.
Coolant does have a sweet urethany smell to it. Was the heater core housing cleaned out when core replaced. If done at a dealer, probably just wiped it out with a dirty rag. Pull the cover below the right side dash and spray it full of dish washing soapy water, heater core and all, and rinse, it should drain out the condensation drain and you will now smell the flavor of dish washing soap you used. BTW, heater core replacement is not that hard for DIY'er.
My C9 inj sleeves started leaking at 723,000 miles. If you have an injector cup leaking, you will see the color of the coolant showing up in the fuel water seperator bowl as it does not mix with diesel. My Racor see thru bowl had red coolant Cat uses contrast well with the green diesel. Also, you will get diesel in the coolant, you can pull the recovery jug cap (careful when hot) and look for a milk shake sludge on the bottom side of the cap. U will also see some dribbles of diesel floating on top of the coolant. I then pulled the injectors and did a coolant system pressure test to verify sleeves and nothing more serious like a head gasket or cracked block or head. Sure enough, I could see one sleeve slowly dripping coolant into the injector housing. If your motor has never been over say 240 range temp, you probably do not have anything cracked.
I researched replacing injector cups online and found many Power STroke utube vids DIY'ers. I bought my injector sleeves and o-rings, went to Star Bolt and Screw in Little Rock and found a 1-14 Taper Tap that fit nicely into the sleeve, welded a bolt to the top, ground off some of the taper to keep it from bottoming out in the sleeve, bought a steering wheel puller and made a make shift sleeve puller for around $45 (Cat wanted $600 for a puller and I could not find any aftermarket). Pulled all six sleeves with my make shift puller (be sure and catch the metal filings from the tap so not to fall into the cylinders, I used one of those plastic push/ pull fasteners like is found in older auto door panel assemblies, some use a coin, and then vacuum out good.
None of the sleeves were cracked, but the leaking sleeve had obvious trash (black something) smeared against the o-ring, probably there from new, causing the o-ring to leak. All the sleeve's o-rings were becoming brittle which is understandable being located that close to the combustion chamber temps. To do this, you need to know how to pull your injectors, research as you need to drain fuel and oil from the rail first. You don't need expensive injector puller tools, I use a small 90 degree pry bar and socket for a stand to pry the out.
It did take several flushings to remove the amount of diesel that accumulated in the block, trans cooler and radiator, just keep flushing untill water is clear. I bought radiator flush for this, but I like the Cascade idea to save a little. I pulled the plug on each full tank and found no coolant in the bottom of the tanks.
A couple six packs later, back together, sobered up and running down the road now with 846,000 miles. Did not have to replace injectors or injector pump. I do, however, clean injector tips from time to time to unclog the nozzles.
If your truck is running good and not smoking horribly, injectors and huei pump are OK. The diesel in the coolant, and coolant in the diesel did not cause any performance issues. All of the coolant was apparently caught in the fuel water separator. You mentioned your truck is not getting hot and running good, I bet a dollar to a donut you have some injector sleeve o-rings that are toast.
Hope this helps.