Car audio....Both rcas work but not together?

Aite I got 2 12in jl w1s in a sealed box with a interfire ib4700c 4chan amp and a jvc head unit and have the amp bridged to 2 chan.....I got my system installed professionally at a shop in clovis and it was thumpin hard but then after 3 months it wasn't hittin as hard so I unpluged one of the rcas and one the subs slap harder then both of them so wtf do I do plz help