Forced air fan (heating/cooling) runs only in hi-speed position.

It'd be unusual to have this problem in both heating systems at one time, but it sure sounds like faulty blower resistors or switches to me. An auto electric shop or a Dodge specialist may be able to help you. If you want to find a Dodge specialist, here's our directory link for you: https://repairpal.com/dodge-repair-in-huffman-texas