Just replaced the heater resistor and the blower motor. I still have two issues:

1) The fan seems to run pretty slow, even when on high speed.

2) There is barely any air coming out of any of the vents

I'm now feeling like I need to dig into the heater box itself to get to the flapper doors and replace the core while I'm at it. I've seen write ups and pics for non-a/c trucks, but mine has a/c.

As for the slow fan speed, I'm thinking the switch on the dash is the only thing left. I'm surprised how hard it is to find one however.