Well, the new cap didn't seem to do anything. Hose is still hard after sitting. I also let the truck run for a bit with the cap off and noticed small bubbles at the bottom of the tank. Also, it does appear to be losing coolant, I can't keep the coolant level steady to save my life, weird thing is though, the overflow tube stays dry so I'm not 100% it's coming out of there? Is it pretty certain that the gaskets are bad or could it still be injector cups? I just don't want to spend any $ on things I don't need, money is tight right now. I guess the silver lining is the labor won't be much more if I have to do both at the same time.
You didn't reveal any of the truck's history, other than an approx odo reading.
If this is a "new to you" truck then there are many unknowns.
1) It seems to have been "topped off" with straight water, or you wouldn't have a frozen solid top hose.
2) If #1 above is true this has been going on for some time and you are obviously down to a very low concentration of anti freeze.
3) This may be PART or MOST of the reason that it was sold - maybe.
At that mileage it is quite possible that your water pump is gone/going.
As some of us (now, with 20/20 hindsight) know, if you are doing injectors it can be a good idea to do the water pump while the truck is apart.
Look for leaks just behind where the lower rad hose goes to the engine.
If you aren't familiar with the anatomy of Duramaxes it will seem STRANGE that the water pump is THERE and not immediately behind the fan with a belt drive.
Nope, it is gear driven from the rear and ONE of the studs that hold it in is hidden behind the harmonic balancer, so it is quite a strip job to get to and replace.
See other threads on water pump replacement, etc.
PART of the GOOD thing about doing these together is that once the fan is off and you have the valve covers removed you can do valve clearances, which you SHOULD at that mileage - easy to turn the engine over with the harmonic balance bolt and you can't get to that with the fan on.
I got a Gates pump and housing from Rock auto about a month ago for under $80 with shipping, so don't believe the older threads about water pumps costing several hundred $$s.
I don't have the number handy, but I posted it in one of the water pump threads.
EDIT:
Gates pump 42349BH
:END EDIT
It is a quiet pump, none of the noise that others have reported on other brand pumps.
Good luck.
EDIT: I had meant to say LOOSEN the harmonic balancer bolt and then tighten it back in LIGHTLY before getting too much else off.
I used the "bump the starter" method, which is probably frowned upon by some, but it worked.
After that I could disconnect the batteries and get to everything else.
With 20/20 hindsight I would probably do the water pump FIRST (assuming I knew it was bad BEFORE doing the injectors, I didn't know that).