Smells like bad sparkplugs, I don't know about this car, but my conquest hates all but maybe 3 sparkplugs. Some sparkplugs for some reason just don't work with certain cars. Get a new set of sparkplugs regularly used by other owners, check gap and try again. It is possible to get crap plugs brand new.
2003 GMC Sierra SLT 2500HD CC/SB