I got a 2002 Ford F150 5.4L. Every once in a while my truck will rev up and down. And also the heat will blow hot air but not all the time. Sometimes it's just warm. Are these two issues related or two separate problems?

 

I think they are separate but we would need more info.

For the rev up, check the main vacuum hose at the rear of the engine on top. That sleeve wears out and causes issues.

Many things can effect the heat, blend door, low coolant, heater core blockage. There are several articles on here with these symptoms. Let me know what you find out.