I have an older GE Dryer and it doesn't get very hot. It takes over an hour to dry a small load. I've cleaned the lint trap and that's about it.

Clean the blower housing on the inside. Clean the vent exhaust from back of unit to where it exits the house. Problem Solved

Assuming that this is an electric clothes dryer.

Probably defective heating element or high or low temperature sensor. Repair can be done by a reasonably competent handyman type person.
Diagnosing burned out heater is easy, you can usually see that the heating coil is burned into. If not check with an ohm meter. Determining if one or both of the temperature sensors is defective is a little more difficult.

Unplug dryer. Lay a blanket or some other soft material on the floor in front of the dryer. Turn dryer over on its front. Remove back panel. Look for heating element, will have to fairly large wires going to it. Disconnect wires. Remove the 2 or 3 small screws holding in place. Remove and examine it. The element itself will look like a spring and will probably be enclosed in a metal frame. If element is broken that's you problem. Replace. The elements are fairly generic and can be found at appliance parts stores. If heating element appears to OK and you suspect temperature sensors, I suggest that you just replace both and not worry about determining which one is defective. Temperature sensors will be round, about 1" in diameter and about 3/4" thick.

Footnote.
Should you decide to replace rather than repair, most older dryers used a 3 wire hook up. Some new dryers require a 4-wire hook up, some can be either. If you replace with a 4-wire you may have to have electrical work done.