My dryers keep breaking heat stops after 5- 10 minutes

I have had 2 gas dryers both have broken in the same way after I worked on the last one I finally ended up getting rid of it... actually still in the back of my shed. anyways I've tried changing the heat elements, and both of the safety kill switches. I cleaned us the entire dryer and the exit hose (only 2 feet). anyways I got another dryer (moms old one) cleaned it out before installing (also gas) it worked for about 6 months now the exact same problem is happening please help, it is in the hardest little spot.