[GTP Racer]

i have a 91 5.0 and recently it has had problems starting.. I have a brand new Powermaster 140amp alt. brand new 6yr. battery, new msd ign cap, rotor, wires and plugs... i dont know wat the problam is.. my battery is dead everytime igo in the car even wen it was JUST running like 2 seconds before... the car starts up on jump so i dont think it could be the starter.. but who knows it might be.. someone please give me answers....also wen i am driving my volt gauge is really low and all my lights r dim but brightenup weni give it gas... i thought this was alternator so i bought a new one.. i don't kno...