Tempermental Starting

I have a 2000 Chevy s-10 pickup and I have a strange problem with my fuel system. If you gas tank is below 1/4 full my truck won't cold start. If its been running it will start again fine and I drive it below a 1/4 tank with no problem. If it is above 1/4 tank it will start fine. I have had times when it would not start and putting a bit of gas in it from a red can had it starting up right away. I had a mechanic check the pressure from the fuel pump and it seemed to be fine at the time. Been living with this for years now and it has not gotten any worse. Any ideas?