ascending for me comes easy, but when decending i tend to have a hard time putting the tips of my fiingers on the string and it'll be the flat part of my finger that hits the string, thus created a muted sound. also, it's impossible to avoid contact with the strings over the one i'm fretting.

this is generally when playing scales.

should i just practice slowly?
Sounds like you need to clean your technique up a lot. It takes a lot of practice and hard work to get those fingers doing what you want. Its hard to give someone advice when you have never seen their playing, but from what you have wrote I think you need to start working very hard on finger control, and independence.
What helped me most in that department was practicing lots of legato, fast scale runs, and using the four finger rule. You can learn more about all those things by searching a bit.
action is insanely high, and it doesn't get any lower. crappy OLP. Ibanez for christmas.
the hot weather doesn't help either (sweaty hands & fingers) ...
but i only just found this out when i tried to improve my speed... so far i've never really even tried to play faster stuff.