what i wonder about those alum-cleanable filters is do they have a good anti-drain back and what micron is the screen? something that can be done to check whether it's filter drain back, or some mechanical issue is to simply try a different brand of filter. i don't like wix, k&n, mobil one, and sadly baldwins. i'd find one of the red purolators and try it. they're inexpensive and would make a good first step test. if you notice a positive step in the right direction then try some other different brands. you might be surprised at what you find.