Blower goes from dash vent to defroster

The problem is that you have a vacuum leak and when you put the engine under load and the vacuum is lessened it switches to defrost cause it takes less vacuum. Now a vacuum leak can come from many places, hole in a vacuum line a blown plenum gasket, even a check valve that has gone bad and there are 2 that I know of. I cant tell you exactly what your leak is coming from but I would check or replace all vacuum lines first.

I had a 1994 Dodge Ram. The Red Dodge Ram I had it malfunctioned and my brake became the throttle. I had to put the truck in reverse then park. to stop, after it was out of control at 80 mph a hill slowed us down. Are you sure its not electrical and the curse control is not giving you trouble? Mine had multifunction switch was not working and the headlight switch burned up. I also found out that Audi had problem with the brake becoming the throttle in the 1980s Daimler Chrysler and Audi were German made. I don't think there is an easy answer. I hope you stay safe. Another man is having strange trouble also. I'm sure there are many more people with trouble with the vehicles. I wish Dodge would step up to the truth. and recall their nightmares. I saw many of their 1996 Dodge trucks at their dealers shop with all the electrical pulled out.