'95 RAM 1500 - No Heat!

I've had the truck going on 5 yrs. Never had great heat, but it's getting worse. Now it practically has no heat. What little there is comes when it is
idling. Start down the road and it's cold air.
SYMPTOMS: No heat (very, very little anyway) when moving. SOME when idling.
WHAT I'VE DONE: (in the last 6 months) + New Radiator + New water pump + New thermostat + New heater core
ADD'L INFO: Both heater hoses are hot once the truck is warmed up. A bit warmer air when you turn it to "recirculate".
I'm wondering if it's a vacumm leak somewhere. Is the heater control/blend door vacuum operated?
Truck has 290,000 miles. Never been to a dealer since I've owned it but I'm throwing in the towel. Have an appt next Tuesday but if ya'll could help me before then I'd appreciate it!
Thanks!
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Bob wrote:

Most likely the door controls. They are vacume operated, but there's a mechanicla linkage to actually move the doors. If the core was replaced, I'm surpised nobody inspected the box to make sure everything was working correctly.
--
.boB
On Order: 2006 FXDI, Red.
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Ummm....that someone was me - and I didn't know enough to inspect it ;-) Looks like I may be going back in. Thanks!

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The mode door is vacuum-operated (selects defrost/panel/floor vents). The blend door is mechanical. It's spring-loaded, and a steel cable connects to the dial on the HVAC controls.
Remove the dash bezel (two screws in the cupholder, two in the ashtray), then remove the HVAC control (3 or 4 bolts/screws). Disconnect the cable from the control on the back, and tug on it gently. You should feel some tension on it. If it goes slack, the blend door is probably wedged. To repair that means removing the HVAC box, and that means recovering the A/C, draining the coolant, and removing the entire dash. Not a very fun job...
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Excellent reply. Sounds like I'll be going back in. I've exhausted all other options. I've never had the truck to a dealer - always done all repairs myself. But this one has me stumped. My wife says "take it to the dealer". Then I told her of a couple of stories on the 'net similar to mine where the dealer charged $1,000. She changed her tune and wants me to give it one more try ;-)
Thanks for the advice. Sounds like I'm going to take the dash/HVAC out.

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