I'll start by saying I'm not much of a car guy... I bought a 1994 Suburban 7.4 L a year ago. 87,000 original miles. Took it into the mountains and it was missing like crazy coming up the mountain passes. Seems to idle just fine, seems to drive fine in town going under 45 mph. Any advice on what to try? Onlything that comes to my mind is getting new plugs and wires.