Truck won't come up to operating temp after rad install

[Andrew]

I'm currently trying to understand why my truck will not come up to operating temp. I recently installed a griffin rad (1st gen s10) The original rad was a dual core and quite small. This griffin rad is much larger, aluminum and a triple core I believe. Ever since the install my truck will not come up to full operating temperature when I'm driving. If it's sitting there idling in the driveway it will very slow come up to 190-200F and then the electric fans come on. When I'm driving it will barely ever creep over 160F. I've replaced the thermostat twice (third on now) and that is definitely not the problem. The current thermostat is rated at 192F. I've tried blocking off the rad almost entirely with cardboard just to test it and the temperature will not rise above 160 while driving. I'm kind of at a loss at the moment. The engine is a roots blown 3.2, if that makes any difference. I feel like I'm having a can't see the forest for the trees moment here and would love some input/suggestions.