** I pulled the dryer out and the vent was clear, but I have not gotten outside to be sure air is coming out. **
It must be clear all the way to the outside, not just from the dryer to the wall.
** The clothes move, get hot, but it just takes forever. **
** Is it difficult to replace a heating element? **
The heating element is the thing that generates the heat. If it needed replacing, your dryer in most cases wouldn't heat at all. If a GE dryer, it is possible for one of the 2 elements to have failed but most other brands, not.
BTW. How hard it would be to replace depends on the brand of dryer and how it was designed. That job goes anywhere from not too terribly difficult to having to take the whole dryer apart to even get to it.