A Model Number may help other help you.

You need heat and air flow for efficient drying.

Air Flow
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.
Also the above is NOT recommended for a gas dryer due to possible carbon monoxide problems.

Another thing to check is the lint filter. If you use fabric softener it can coat the filter, greatly reducing air flow. If this is the case clean it with soap and water.

Heat
Does the unit provide different heat outputs with the different temperature settings?
If not then you probably have a heating problem.