Engine is cold

[shrike]

ok, first a little backstory:
I had the truck last winter, with the original heater core and 1 speed on the fan (basically on or off) and it seemed to warm the truck adequately. I also had no working temp gauge.

This summer, I installed Vintage Air (which includes a new heater core and fan) and put a new intake manifold on (including a new thermostat) and installed a temp gauge.
ever since then, the temp gauge read really low unless I was sitting in traffic for like 30 minutes in the summer with the air on. Then it would creep up over 200. Most of the time it would run at 150 or less.
I thought it was possibly a bad temp gauge (and I am going to replace it, Im not happy with it for other reasons) but just lately we have had a cold snap (in the 30's) and the heater will not blow even warm air unless I have been driving the truck for 45 minutes or so and the gauge reads at least 150. Most of the time, driving around town the gauge is sitting at the bottom, not even moving and the heater blows cold air.

I am guessing the thermostat is either defective or installed wrong but I thought I would post and see if anyone else had any ideas.