Thanks for the comments. I pulled the dryer out and the vent was clear, but I have not gotten outside to be sure air is coming out. I do have a bend in the vent - the dryer sits up against the wall, and the opening in the wall is about 6 inches above the opening in the dryer. Because of this, I thought surely the problem was lint build-up, but that's not it. The clothes move, get hot, but it just takes forever. I will try running it without the vent as a test. Is it difficult to replace a heating element?