Truck won't start every time but probally 95 percent of the time.

I bought this truck about a week ago. It is a 1996 Chevy S-10. It has a new 4 cyl that was put in about 50,000 miles ago the reciept says anyways. This has happened to me three times now where I can drive my truck somewhere and it would run fine there. The next morning or even like 6 hours later I will hop in it and it will crank and crank but just won't fire up. I poured a little gas into my air intake hose and everytime I did it would fire right up and run until that gas I poured in there would be gone. Only once has it ran good and I shut it off for about two minutes and started it back up and drove off and it sputtered and died. I got it to fire back up but had to keep slamming the gas pedal to give it a little gas at a time to sputter all the way home where it died again and couldnt start it till the morrning. I believe it is my fuel pump I want a second opinion and also info how to replace the pump if it is that.