Background info:

1980 Camaro Z/28

Rebuilt 350, slightly bigger cam, holley 600 carb, edelbrock intake manifold, hedman headers and exhaust.

Overheated really bad transporting it halfway across the country around 2 years ago, fixed it after an hour of driving by replacing the flex fan with a bigger one (15" to 17") that fit the shroud much better. Fan is inside the shroud at most a quarter inch, and that's with a 4 inch spacer.

Problem:

Once I start it up to drive somewhere, the engine climbs in temperature normally, but then goes past the middle ideal mark (210) and keeps climbing until it's right on the edge of the redline. At which point I try to let off the gas as much as safely possible to help the temperature decrease. It stays borderline red for about 40 seconds and then creeps back down to 210 and stays there. My first assumption was that it sounded like a slow thermostat (if that's even possible), but I replaced the thermostat about 2 years ago. My current plan is to switch to an electric fan setup, with the benefits of better cooling and I assume less load on the engine due to the better efficiency of the electric motor? But first I wanted to run it by you guys to see if you had any insight. Thanks!