Originally Posted by SuperSentra4203

Correct me if i'm wrong, but if his timing belt jumped even one notch which is roughly what, 10-12 degrees, his motor will run like crap anytime, and prolly have a bent valve.

I'm gonna go ahead and bite the bullet and say you may have uneven or low cylinder compression. Other than that, since it's having issues going uphill or when it's cold, the ignition coil or power transistor is weak or going out. You could just be detonating like hell, run premium for a while and see if that helps. Can you tell if it's running too rich or too lean??