Not Your Average Overheat Question

[mosel70]

'70 C10 396, TH400 3-spd trans, mild cam, 454 heads, timing 36 total
Overheats at low speeds or at stops. If I go straight to highway at 65 it is fine. If it overheats at low speeds and then I hit the highway, it won't cool down, stays in the red. With rad cap off, I see good flow in radiator. With engine warm, in gear at a stop is 700 rpm, but in park it goes to 1800-2000 rpm.

Here's my question: With temp in the red, temps on both ends of lower AND upper rad hoses show 210-213 degrees. No 10-20 degree difference. Why?

New:
Mishimoto 3-core rad
Mishimoto twin puller e-fans, 2600 CFM; 1x 1100 cfm pusher fan
2x gauges
2x temp sensors
rad hoses
2x water pumps (clockwise looking from front bumper), FlowKooler
trans cooler inside rad
Edelbrock 750 carb, mixture screws turned 1 1/2 turns out
Edelbrock RPM Airgap intake manifold
HEI distributor
Hooker headers
Rear gear ratio 3.73