Temperature fluctuations

Last week I noticed while on the highway my temperature gauge (which is and should remain on cold due to fan wired into the ignition to keep the engine cool, no air conditioning, previous owner originally had it wired to a toggle switch, but we moved it so I didn't have to worry about turning it off and the toggle broke). Anyway, I realized that it was reading slightly above the middle, but it wasn’t constant like in a normal car. It was going up and down. It was happening at random times not just at acceleration or when I decreased speed or when I maintained it. It wasn’t getting dangerously high, so I didn’t worry too much. Assumed I needed to replace the fuse the fan is wired into. Well, the next time I took it on the highway it began doing it immediately and this time after fluctuating for a little it started to get too high so I pulled off the highway and checked the fuse. The fuse was fine but I replaced it anyway. The fan does run when I start the car. Now it seems to start going up after I've come to a stop light, and it doesn't take much. Within minutes and well before the engine is “hot”. It did stall about a month ago and after I replaced the fuse it was a rough start with a rough idle to it shaking some. That eventually stabilized. However, I've had some issues with starting it on and off for a little while where I have to press on the gas a little to get it running. The fuel pump is less than a year old. Oil was changed not too long ago and has enough. The fluctuation on gauge is where I'm confused. It doesn’t really change when I'm at light like it would normally if it was actually overheating. It only seems to do it when I'm driving. It does return to cool after it is shut off. I think I got everything. I think it is the ECT but wondering if it could be something else or if I should be checking something else.