2000 Toyota Camry occasional engine misfire

A while back it was recomended that the spark plug wires be replaced based on the mileage. The second set was defective after only a very short time. They were replaced at no cost. Now, after about 20,000 miles, I am having an occasional "miss" in the engine, specifically on a long upgrade at a constant speed, or at least that is what it feels like. It starts fine, idles fine, and accelerates fine. So far no check engine light has come on. I dare say the garage installed an "adequate" set of plug wires which were from the same manufacturer as the failed set. Would a better quality set of plug wires be my best fix or could it be any of a host of other possibilities and best be checked by a qualified mechanic? Tnx