perhaps this was simply adding a maf sensor to a stock 95 mustang 5.0 it would make no sense to just install that without supporting mods. it would be similar to adding a 3 inch muffler on a stock 1.5 exhaust its done absolutely nothing and perhaps hurt power. although im by no means a expert. basicly every car needs 3 things to make power air fuel and spark. too much spark does nothing without fuel and air. to much fuel hurts power and the same with to much air. i dont think this will affect your car and you probably did gain power you have supporting mods.
if anything the lesson i learned reading that was that i would be better off amassing a large amount of after market performance parts installing it all at once and tuning it. itll probably put a bigger smile on my face getting a all at once 50hp increase than a progressive increase 5-10-15hp increments