no power before 3000 rpm

hey first time ever on one of these web sites, so i hope i'm in the right place to ask . 90 5.0 aod dart heads x-303 3500 stall msd 6al, 70mm t-body 75mm maf edelbrock rpm intake 24 lb/hr injectors 4.11 gears full exhaust nos big shot. of the bottle this car runs like a dog until 3000 rpm then it comes on strong. i know it's a big cam for an aod but it used to have good power until recently, checked plugs wires, cap rotor fuel pressure at 32 psi timing at 12 initial changed filters don't have any codes showing. lost and frustrated any help or ideas would be greatly appreciated!! thanks again green salad up

thanks for replying , it is an obvious lack of power, with a lot of sputtering and an ocassional poping or backfire , no noticeable smoke from the tailpipes , plugs are light tan, and almost like a light switch at 3000 rpm it clears up and it's gangbusters. to clarify the converter flashes about 3500 rpm on the juice, 2200 brake stall. any advise is greatly needed! gsu