1998 K3500 5.7. Misfire with no codes. Idles fine. The misfire starts at about 1400 rpm to about 4500. It clears up with high throttle and wot. Replaced all plugs, wires, cap, rotor, distributor, coil and ignition module. Changed a fuel filter but i really dont feel like its a fuel delivery problem. Im a ford guy and new to chevy. Any help would be appreciated, im really out of ideas for what to do to fix.