truck wont warm up

[hillbillyrider]

94 2wd with 4.3. I have only had it a couple weeks. It will not warm up enough to get good heat. Replaced the t-stat and still won't. Put a half of pizza box in front of the radiator and it still won't. It barely gets off the 100* mark and i am tired of freezing. With the cap off I can give it some gas and watch the coolant level go down. Top rad hose gets hot, bottom little warm. Heater hose in rear gets hot, front little warm. I don't know the history other than the engine was supposedly changed out. But the one they put in is supposedly a little older model. In the pic below it had been idling for 45 minutes. It never get warmer than that.