Dryer taking two cycles to dry clothes

Dryer started taking forever to dry clothes so I started looking in what the problem could be. The vent is not stopped up and the fan is working properly. What I do no is with the drum out and the dryer running on more dry after about 1 min one of the elements shuts off and after about 5 min the other shuts off. after running another 5 min or so one of the elements turns back on but not the other. Can someone tell me if that is normal. I do know that it is the 4 wire high temp thermo that kicks off when half the element goes off. Any idea’s??