Got a 96 EK Sedan DX with a stock y7 besides a dc header. Recently I've been noticing that my car starts to slowly get a little hot on a 20+ mile drive on the way to work. It only does this if the AC is on and it's above 95 degrees outside cause when I drive it at night even with the AC on, it doesn't heat up even slightly. I've ruled out several things it could be.. My coolant level is great, right where it should be, water is flowing through the radiator consistently so it's not the water pump, and my radiator fan is on all the time cause I have the switch jumped, and I have no thermostat, so that's not it either. If it matters, when it starts heating up, I can switch it to the heater and the temp drops instantly back to where it should be; so it's hardly overheating cause the temp drops right away. What could it be? Should I do a system flush?

 

That points to a partially plugged radiator core. With an always on fan AND no thermostat to restrict flow, it would seem, you are not using all of your core.
Try a good flush first.
Then, repair the items that are making you use an always on fan.
And then,put in a thermostat.There is no way to accurately diagnose cooling problems if the system has any expedient fixes in it.