dryer warm but not hot

unsure of model number. dryer is not getting hot, it takes several cycles to dry clothes. looks as if some of the coils are working but not all. do i need a new element or thermostat? thank you

Need a Model Number
http://www.appliancepartspros.com/modelnumber_locator.aspx

Some units have 2 coils.
If yours is one of these perhaps one coil is burned out.

Here are your parts
http://www.appliancepartspros.com/partsearch/model.aspx?model_id=265780

Here is the tech sheet
https://www.servicematters.com/docs/wiring/Wiring%20Sheet%20-%208528187.pdf

Could be just a vent problem
Undo the dryer from the exhaust
Run a load
If the load dries correctly then you have a vent problem.
Clean/check the vent system. Make sure the outside louvers open fully.

If you do not want lint in the house.
Take a pair of pantyhose, put one leg into the other and attach this to the dryer exhaust.
Leave enough room behind the dryer so it can blow out like a windsock.
Run a load.

Both the above will allow you to check the air flow and temp.

ran dryer with vent off yesterday no diff. runs warmer with nothing in it as soon as clothes are put in the temp. goes down.