[00GTP*LIFER*]

Okay I am in serious need of a starting point to hopefully tackle this problem. I have a 2000 GTP, 164,XXX, I just bought it with 155,XXX( i was my own salesman at the dealer i worked at). No after market mods.
Okay so car ran great started everytime no struggle then one day i stopped for about 10 minutes and when i came out and tried to restart the car it started then chugged itself to death about 20 seconds later and would not restart. I gave the gas tank a few bangs and it started right up. I put a bottle of lucas fuel injector cleaner and full tank of 93 octane(ALWAYS by the way). Problem went away. Happened occasionally for the next week. Well it was fine since may now last week it started again only this time the bangin on the tank didnt seem to work, after about 6 or 7 failed attempts it started and was fine for a couple days. The last time was the other day it was difficult to start all day then finally stalled at a light and would not start up. Got it home and went the next morning to start it up. would just crank but not turn over. put a jump box on it and it started but wont stay runnning more then five minutes without chugging itself to death....any advice???