engine misses when pulling a hill but runs good at high speed

Possible Plug wire or coil problem

change fuel filter

review when last tuned. may need to regap or replace plugs(rec. premium). inspect ignition cable. may need to replace. rec. performance grade such as accel super. they are more cost effective than OEM replacements. also reccomend ethanol treatment for fuel system. this will clean system. ethanol blend in todays fuel creates build up in fuel system and combustion chambers. it also causes excessive wear on spark plugs. 1 tank premium with ethanol treatment every oil change should do.