1991 Chevy Caprice 1991 Chevy Caprice hesitates and stalls.

I have a 1991 Chevy Caprice when I try to start. It wont start the first time. I will turn it off and try starting again then it starts. Then idles strange I will put it in gear it hesitates and does not accelerate properly and sometimes stalls. When I press on the gas it is very erratic and if I let off the gas it wont stall. If I press gas harder it will stall out, but starts right back up. The problem started it would only hesitate at first acceleration only for a split second then would drive fine. All of the sudden it got worse and started doing this. I changed the spark plugs and air filter before it started doing all this. I just want to get some feedback before I do anything else to it. I do not know if it would be the fuel pump, vac., or what so any advice would be appreciated.