Electrolux gas dryer melting clothes

The heat vent in the back of my dryer has a build up of charred black stuff and melts clothes. I use only medium or less heat and quit using fabric softeners. I had the vent replaced yesterday and after drying a few loads of clothes, can see the black stuff beginning to build up again. I spent a long time on the phone with Electrolux and they are sending me ‘other parts’ to attempt to fix the problem. When I googled this issue I found multiple complaints, but no solution. Do you have any ideas?