1997 Ford F-150 4.2 Idles Rough

My truck keeps giving me the P0174, P0302, and P0303 codes. On rare occasions I get a P0172. I have replaced the 2 Front O2 sensor, TPS and Catalytic Converters. I have also cleaned the MAP, MAF and the IAC. I get the 303 and 302 codes at idle or low RPM. When I am driving at abour 55-60 is when the 174 code shows up. I have checked for vaccum leaks by listening for them and spraying starting fluid on the vaccum lines but I cannot find a leak. I hope that you would have some advice on what I should check next. I have a diagnostic code reader but it does not give me much info. I can get the fuel trim and that is about the most advanced info I get from it.