Are you running the stock diameter crank & water pump pulleys? Can the air coming into your grill go around the radiator to get past it without flowing through it? Sorry, I posted before reading the guys posts, which are on point. I also agree it's likely the electric water pump.
Yes, vacuum advance beyond the 35* total will allow the motor to run cooler at road speed. If you switch you ignition box to a programmable one like the MSD Programmable 6, I believe you can add a simulated vacuum advance feature, but I have not done it.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
| 
