Kenmore Elite Electric Dryer - Inconsistent Temperature

Greetings!

Here's the situation. We do lots of loads of clothes each day in this dryer. Over the past six months we've started to have a couple of problems with consistent drying times.

1) the temperature settings work inconsistently. The towels setting, the warmest setting, drys about 200% longer than it used to. Other settings, Express, Jeans dry about 110-120% more time as in the past.

2) the first two to three loads of the day drying at the selected dry level works fairly consistently, taking about the same amount of time each day for the save dry level for the same selection of clothes. Over the rest of the day the subsequent loads takes exponentially longer to dry. Selecting different settings with these subsequent loads during the drying process, you can coax a little more heat but the loads will take 200% more time than the first two-three loads in the morning. Each day we experience the same cycle. We clean the lint filter between loads and two/three times a day we check to make sure that we are getting good air flow out of the outside vents.

Any idea what might be the problem?

Thanks,
Hpnutty