blazer runs to cool

[6768chevylover]

I have a 71 blazer with a 350 that runs to cool in 60degree or less temperatures. It will heat up of course if I was to sit in one spot with no fan on. Once I start to drive the temp goes below 150 and then there goes my heat in the blazer. I was looking at underdriven pulleys to slow my water pump down. Right now my water pump pulley is about a 7" and my crank pulley is 6.75" which is underdriven but was looking into a smaller crank pulley of about 5.5". Would this slow the water pump down to heat up the water in the block more?