1991 Toyota Corolla engine hesitates and stumbles at differ

Well this seemed to happen rather quickly not over time. The car is hesitating or stumbling now, it seems to have a gargling sound now. Its not all the time though, when you step on it good it happens but after you get it going and let off the throttle and sort of ride it the engine goes back to normal and even lets you gas it some times alittle with out problems then on till you hit it harder again. I changed the fuel filter, plugs, air filter, and cleaned the injectors. There is an after market intake and muffler and there has been exhaust leaks for almost a year that has not affected before.I believe there is an after market intake that does not have an egr valve, so I dont think its an egr issue. Any ideas