Dove my car yesterday no problems at all. Start it up today and it sounds and runs like crap. Will idle fine, and above 2000RPM drives and sounds fine. but between those ranges it sounds like an old pos caprice from the 80's and has an occasional backfire. Should i replace the spark plugs or what do you guys think this sounds like?

car is 94 formula, LE2 heads, cc306 cam, and supporting mods