1994 GMC Yukon SERVICE ENGINE SOON light

I suggest changing those wires and plugs for A/C Delco. Your ignition system produces a higher than normal voltage 50000 volts or so. A/C Delcos' Platnium plugs and wires are designed for this--and--they are what was on your engine in the first place.
Yes, the autozone guy will hook a scanner up to your computer plug and see the trouble code. The code will have a letter followed by 5 numbers -- like P0302 or something like that. They do it all the time and the best thing is it is free. A mechanic will usually charge for this. The trouble code will lead us in the right direction.