Are you having any issues with the oil pressure sending unit, the one wire from the sending unit splices into the power wire for the fuel pump. I can't believe you aren't blowing the ecm-b fuse. There were some vehicles that had the in tank fuel pump connector melt, but you replaced the pump. Have you tried using dielectric grease on the contacts for the relay, corrosion may cause some of the problem.
A 4 post relay will work on that vehicle, the fifth post is for the fuel prime connector and is used only for testing the fuel pump with the truck off