I have a whirlpool dryer wgd5300sq0 and it is taking too long to dry the clothes. After the dryer is started, when I open it to see if the heat is coming after 15-20 minutes, I do not feel the hot air. Only after a while (may be after 45 minutes or so), I feel little bit of warmness. but even after that it's taking almost 2-3 hours. Can you please advise on what other steps can I take to troubleshoot the issue?

I have already opened up the back of the dryer and cleaned it up entirely. In addition, I have also cleaned the outside dryer vent with the lint eater tool you suggested above. But still my problem is not resolved.