2000 silverado hard to start (sometimes)

Hi Guys I got a wierd one my 2000 silverado 5.3 normaly starts great but when you lease suppect it it takes about 15 minutes to start, it turns over fast but just wont catch I have unplug the mass air flow sensor  but that didnt help I sometimes put a battery charger on even though I have a new battery and i think that helps it start and afther it does starts in runs and starts normaly for a month or two then it happens again   any ideas Thanks

you should check to make sure you are getting gas. ou should check the fuel pressure it could be your fuel pump starting to go

Thanks 74 chevy  I will do that although I replaced the fuel pump and filter when my gas gage sensor messed up because they came as one unit