Good question, seriously- I wish more posters would include detail like you did.
Blower is running - eliminate electrical.
Changed t-stat and heater core. We can eliminate lack of hot water supply and a fouled heat exchanger. Hopefully - disregarding any "bad out of the box" issues.
The motor runs at normal temp but it does go down quite a bit when i turn the heat on.
The fact that engine coolant temp drops noticeably with the blower in operation would eliminate flow restrictions in the heater core's supply and return hoses. Also confirms proper heat exchanger function.
The only other things you could have mentioned was whether there was a significant difference in the temperature of the hoses (supply hot/return cool) and that you had popped your radiator cap and confirmed lots of coolant gushing into the outlet tank from the return nipple.
Anyway, it seems that plenty of BTU's are being delivered to the cab's air-handling system. But the air-handling system is not delivering those BTU's into the cab:
The first reaction to improper temperature from the vents is generally; "blend door problem". Might as well start there - it's easy:
Look under the dash - behind the glove box. You'll see the plenum. Assuming you have A/C, it will look like this (the red line is supposed to be the cable to select hot or cold):
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Make sure the cable is attached, anchored in it's bracket and can move freely.With the temperature lever in full hot, the crankarm should be all the way to the left (IIRC - you'll figure it out):
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One way or another, get it all the way to HOT and see what happens. Come back and report your findings.
