1979 Other Chevrolet Models Truck won't start

Hi I have a 79 k-10 scottsdale. The problem I am having is if it starts it dies when you give it gas. I replaced fuel filter and when I did the truck will start and stay running and you can rev it and its ok but when you put in drive and try to go it dies then won't start. I have purchased fuel pump but have not put it in cause I was told its the vaccum system. So this is the confusing part for me this morning I started it and drove it. It drove fine when it was cold then after few minutes when went to acc. it died then wouldn't start. Is it the fuel pump? Thank you for your time