Hey all, I haven't been around much the past couple years, as I bought a Ford back in April of 2010. But, I need some help with a buddy of mine's truck. He has a 2003 Sanoma ZR2 4x4 with the 4.3 with roughly 56k miles. He called me up yesterday, saying his truck was overheated on the way back from school. I went over to his house today after work and went for a ride with him It heated up as normal to roughly 210, or whatever they normally run at. Then about 5 minutes later, temp started to creep up until it got close to 260 and the "CHECK GAGES" light came on. When that happened, I told him to pull over and pop the hood and leave it running. With the hood open, there was absolutely nothing out of the ordinary. No steam, bubbling coolant, etc... and the motor wasn't any hotter than normal (I've been around plenty of overheated engines, and it's pretty dang obvious when they're too hot). It was running fine, idling fine, and showed nothing abnormal. Coolant level was a little low, but nothing big... While we were sitting there, the temp dropped a little bit and the check gages light went off, and then the temp jumped up and the light came back on. We started easily making our way back to his house, and after about a mile, the temp dropped to roughly 235, and the needle kind of jumped back and forth between about 220 and 250 (or whatever you want to call the mark between 210 and 260), and it stayed there until we got back to his house and shut her down. Given the fact that it's running fine and showing no signs of overheating, I want to say it's a wacky thermostat or coolant temp sensor. But I didn't want to say for sure that that was the problem, because I wasn't certain either. So I'm asking for some suggestions. What do you all think? I haven't been around GM's for a while, and have never really dealt with the 4.3, so I don't know if there is some specific problems common to this motor or what.