I get heat and A/C but mostly to the floor vents. Some will flow to the defrost vents when selected, but if I select the front vents, all the flow comes out the floor vents. Assuming there is a switch, relay, etc. that activates a device that opens/closes vents as I move the selector dial. Any help is greatly appreciated! Thanks.

 

Most of the vents are vacuum powered. Blend door is the only exception, and it maybe be cable operated, or by a little stepper motor, depending on year. Think I would look and make sure you have a good vacuum source first, then that the actuators are properly hooked up, and are getting good vacuum. If you don't have a service manual for your truck yet, download one from here.

 

My Ram had a similar issue, the vacuum lines were shot.