Underdrive pulleys and overheating?

I was just looking through the cooling section to see if anyone had this similar problem as mine. But, my pulley set up is a trutrac billet specialties one. It is not under driven, but came with and edelbrock high volume pump. Well since the kit came with that pump, I took my factory one off and installed the whole kit. Well I was over heating like mad, and when I got on the high way it would not want to cool down still. It should of been obvious what the problem was, but I had changed heads, upped the cam timing, and a few other things all at the same time so I had no clue why it was overheating. Well after dealing with it for a long time now and even getting a new radiator. I tested a crossed the upper and lower radiator hoses and it was less than 10 degrees drop in temp with 2 12" fans running at full blast. So just last weekend I got a wild hair up my butt, and desided to swap back to the factory style pump to see if that would help, but still kept the serpentine set up on it. That was a tough task as the factory style one dose not have even bolt hole bosses, and I had to grind them to make it fit. But, with the factory pump back on, it now cools like it did before I put the pullies on, and I can cruise around town again. With the HV pump it was a race to make it to the high way. My guess is that it flowed to fast for the radiator to pull enough heat out of the coolant.