I have a Whirlpool dryer model WED5521SQ0 which is about 4.5 yrs old. Lately we noticed that it takes much longer to dry a typical load. What used to take 40-45 mins now takes about twice that. I regularly clean the lint filter and the anti-bird mesh that sits on top of the air exhaust outside. I also help my hand for a few seconds against the exhaust while the dryer machine was running and it was blowing pretty hard. So I think the problem is not with clogging, at least not outside the machine. What else can be wrong? How do i figure out exactly? Do you think this would be worth replacing or is it time to get a new dryer? Thanks much!