I dont think that the mucus would inhibit thc absorption, but im no doctor. Maybe it is the tolerance like you said, but if you quit for a few days after smoking everyday for a year, and then smoke, you should get really stoned. Quitting for a few days after everyday smoking over an extended period can make quite a difference. I stopped for 4 days after smoking everyday for 2 years give or take a while. After taking 2 tokes I was on my ass.