Hard starting, loss of power

. After it has run for only a few minutes and warmed slightly you can shut it off and when you try to crank it will start, run a couple of seconds, and die. The only way to get it to idle is to press on the accelerator slightly until the rpm's is sufficient. Then you can let off the accelerator and it idles. The other problem is the van has lost highway power and the gas mileage has gone down. I have used a scan tool. No codes are present or pending. The scan tool did say the EGR, o2, and catal mon were inc. Not sure what the tool is telling me. I have also checked the fuel pump pressure. When the key is first turned on it goes to 62 psi then drops back to around 58 psi. While running the pressure is about 56 psi.