94 Gmc sierra missing

I have a 1994 Gmc Sierra pickup with a 350 motor. It has a miss in it when driving down the road around 65 to 70 mph. The miss is most noticeable when starting to pull a hill or when lugging it. The tack also twitches all the time. Just wondering if anybody would know what the problem might be. Thanks

When is the last time the spark plugs have been changed?Also do a compression check on each cylinder.

i haven't done anything to it yet. I don't know if it is a spark related problem or fuel related.