Engine tries to stall out?

Ummm, the fans weren't kicking on, so I had the fuses tested, and the relay's fine, and I hooked the fan motors up, and they worked just fine, but the car would heat up about 220 210, and steam would start building up out of the radiator near the cap.I replaced the thermastat about a week ago, and it worked fine, but ever since i've had new headgaskets put in it, it's temp goes up and down, it used to hit about 250 260, then it would fly back down to about 120 then do it all over again. And i've lived with it, but haven't had it checked out. It's not worth checking out.I bought it for 500 bucks. So.I don't know.I've tried to relieve the fuel pressure by taking out the fuel pump fuse and running it until it stalls, then cranking it a few seconds, then unhooking the battery, then trying it again, but the same things happens, it hits 4000 rpms and stays there. What do you think is wrong?

Well, i've pretty much looked at everything, but I read in a book that I should relieve the fuel pressure before taking out the CTS, but I didn't. And i've tried relieving the pressure now, but no dice.I'll look over everything tomorrow though. Again, there might be something I missed, but I don't think so. Would it matter if I unhooked the sensor on the fuel tank, instead of the fuel pump fuse?

Well, i've checked the fuses, and have taken them to a local auto parts store, and they tested em and said they were fine.