I just got this truck not too long ago, has 148k miles, at first it would overheat after a long time of driving and coolant was spewing out of the cap/near the cap, I removed the thermostatt and that all seemed to stop, but it idles rough and has a cylinder 4 misfire code, all of the spark plugs were changed... It doesn't smoke, coolant isn't leaking out of it but I'm pretty sure some is disappearing, I have to check it again. Any ideas?

 

First thing that comes to mind is a cracked cylinder head and/or blown head gasket on that side.

 

If you put the thermostat back in, start the vehicle cold with radiator cap off, and the coolant shoots up or agitates, you've got an HG leak. You can also rent (for free when you return it) a block tester at any big name auto parts store. Basically, it sniffs the coolant for exhaust gases. If the liquid turns from blue to yellow, or green. It's a pretty safe bet that the head gasket is blown. I've resolved a HG leak without pulling the head, years ago. So, if you need more help, let me know.