Hello,
The problem is in the thermosta and not the element. The thermostat is bad and is cutting off the element before you are getting hot enough..

OR....

There is a problem with the vent being plugged... or the blower not working right...

Check out these tips...

http://www.fixya.com/support/r3866744-dryer_not_working_dryer_not_drying

http://www.fixya.com/support/r3866345-dryer_troubleshooting_electric_dryer_won

Heatman101