Hey guys so, 2-3 weeks ago i took my truck in to get the heater core replaces, as it had a leak and was blowing cold air.
So they put a new one in and all was fine. Today i go to check my fluids under the hood, and notice that my coolant is low, so i open the resivoir and notice its a bit dirty inside, so i open up the cap on my rad, and there is brown chunky like stuff all around the inside, anyone have any ideas?

You've described some a-typical blown head gasket symptoms.

Low coolant without any obvious leaks, high pressures (sometimes damaging heater cores or the rad), 'milky' or 'brown' substance in either the overflow or in the rad itself.

You can check under the oil cap, or on the dip stick for 'milky' looking oil or foam, though most people have to drain it to see. Pulling the plugs and checking for white deposits might be another route to check, or taking the truck to a mechanic with a combustion gas detection kit for the coolant system.

Paul

coolant pressure testers are pretty cheap too. you just hook it up to the rad cap and pressurize the system. if the pressure goes down, you've got a leak...

Man, sounds like a bugger of a problem with a new (to you) vehicle.

Sucks as you were so happy with your purchase

also i have just recently noticed that my temp gauge will from from cold to medium and then back to cold and so on while i drive.
I have a feeling that the "brown" chunkys i found is not a big deal, i think i just need a flush.

But the coolant is leaking somewhere as i see spots in the snow, just cant find out where

Warranty? You just bought the thing, get the dealer to fix it.

i only have a powertrain warrenty

for anyone that cares problem solved, after searching the engine bay for an hour i found a leak in the rad.
Got a new rad and new thermostat and coolant flush...runs mint now, thanks for the help

well glad you got that solved! did dean myers fix it for you?

No, me and my uncle did who is a mechanic for dodge