Truck wont start

1997 gmc sierra 5.7L 192000 kms. truck wont start unless you dunp fuel down the throttle body. When it starts it runs rough then smooths out and idles fine. If you give it gas very slowly you can get the rpm's up but if you dump your foot into it it will try to die but if you let your foot off rite away it will correct itself and continue to idle. Ive replaced fuel pump and fuel filter, I scanned it at the dealership and all that came up was the tps so i replaced it. truck still wont run, Ive checked all possible grounds and connections and wires for any kind of shorts. Also i noticed you dont have to put your foot on the brake pedal to get it out of park, maybe that has something to do with it. I have flowmaster 40 muffler on it, air raid intake, poweraid tbs please help me get my baby running.