TIMING BeLT

how do i know if i need to replace my timing belt? if it looks in GC is it ok? i am at 120K should i do it now even if it looks good? i have had car for 6 1/2 years, DriVen HAAARRRDDD, and i mean RED LIND EVERY TIME every gear, Changed oil at 4-7k miles, replaced Clutch 3 times and tranny once, wtf will changing the timing belt do anyways cept for NOT Break? any other benenfits?


Also how do i adjust timing? i am bout to read haynes manual but i am curious as to the benefits to adjusting timing?
does it affect Gas mileage? (like my cai did, used to get 400 to tank now i get 250 if im lucky) (damn it for trying to hear that thing all the time)

Thanks
Dan