Many times have to turn dryer on repeatly to dry...

Ever since I got my electric dryer last year, it has taken an unusually long time to get loads dry. I use the dry sensor setting and many time have to turn the machine on repeatedly to get one load dry. What a waste of electricity! I have cleaned out the venting, but it does have a about 20 feet to travel. My previous dryer did not have this problem.

Thanks for any advice