Heat too high

Dryer heat does not come down when put on low. All ducts, housing clean, exhaust duct is only 18", straight out. Heating element is not in contact with housing (visual and continuity check). I do not want to just start replacing parts. Is there anyway of testing thermostats? Parts place in Houston checked continuity of all thermostats, but I could have told her that they would have to be at temp to show no continuity. Please help!