Heard Mendez and Moto Perp. yesterday. Just amazing to the point where you want to slap him. But like most greats I'll bet he was very humble, so you can't hate him :) But back to the OPs point. I too was tonguing wrong, anchoring tongue to bottom teeth. I've tried the advice I received on TM, especially to try DIT instead of TU. I'm having the dangedest time with it though. It's like my tongue is too big. Without the mpc I can easily say Tu but as soon as I try to say it/tongue it while playing I have to bend things into an unnatural position, spit starts coming out the sides, etc. The only way I've found is to pucker like I'm kissing or whistling, and that's very unnatural. So...could that be the case, that some people just have larger tongues and will never be able to tongue correctly?
2nd point...the tongue really doesn't act like a piston cutting off air, or rather just cutting off air isn't enough. I whistle quite a bit, and separate notes by cutting off the air with my throat, almost like a cough. Works great, I get distinct notes, and can "tongue" this way very quickly. Doing the same thing with trumpet just doesn't work. The notes are still very mushy.