Cannot get anything past lukewarm air to come out. I've changed the thermostat and flushed the heater core. Blend door sounds like it's working, the actuator is different looking from all the others I've seen though. I've noticed one of the heater hoses feels cold (can't remember which one). Motor temp seems fine. Any help is appreciated.

 

Likely one of two problems:
~ HeatCore plugged: could again try flushing both forward+backward with garden hose; may need new core.
~ HeatControlValve failed: common to have vac tube on this valve get loose\break\leak, though this "fails open"; may need new valve.
If you've got 2way Ford# yg368 VacToClose HeatControlValve pictured below, recommend replacement metal version FourSeasons# 74603

 

Good to include the YEAR of the Ranger, 2002

If one of the heater hoses at the firewall is cold then you have limited flow thru the heater core
Both hoses should be hot after engine is warmed up, one hose can be SLIGHTLY cooler, but just slightly

You can try reversing the hoses at the firewall, this will Back flush the core while driving
Heater cores have no assigned IN and OUT, hoses can be reversed, and SHOULD BE reversed every 2 years to keep the core free of debris to last longer

After warm up turn TEMP **** to COLD
Air temp should change and should blow outside air temp
Turn **** to HOT
Air temp should instantly start to warm up
If so Blend Door should be OK
These generally have a total failure, so temp can't be adjusted at all, no COLD or warm
So if you can adjust the temp it is most likely Heater Core issue, or as Dillard000 said the by-pass valve in engine bay, but both heater hoses should be cold in that case

 

May be air trapped in the HeaterLoop?
Try parking your truck pointed uphill & let it idle until at full temp;
let it cool down, then open radiator cap & see if it needs topping off.
If so then air was trapped.

 

I finally had a minute to look at it again. I tied the heat valve open. I also tried reversing the lines. Neither one helped. I got to drive it and noticed the temp gauge goes down when hard accelerating. Didn’t do that before new thermostat. I also noticed the top radiator hose doesn’t seem as hot as I think it should be. Couldn’t flush again due to my water hose is frozen (it’s cold here).