88 4runner Heater Only works with higher rpm's

Hey All, My heater only seems to put out hot air when the rpm's are up higher than an idle. Is this normal? Its fukin' cold and traffic is horrible here. Any help much thx, ty

I just rebuilt my V6 and now the air out of my heater is lukewarm, UNLESS I take the RPM up above 2500 then it will "burn" your fingers to hold them there!
I have "burped" the heater hoses at the firewall by replacing the stock clamps with "real" clamps then when system under a little pressure I let the air out, but to no avail the heaters still only get hot at high RPMs this includes the rear heater too lukewarm at idle but very hot above 2500 RPM.
I tried restricting the flow through the top radiator hose, thinking it might force more water through the heaters but it still didn't help.

I did replace the by-pass tube under the intake and installed a 1988 3 core radiator that's the only difference. New thermostat too.

900 RPM = 98 degrees F
2500 RPM+ = 124 degrees F

Any suggestions? This ones got me stumped! :confused: