I have a 2002 GMC Savana 5.7L that has multiple misfire codes on the scanner. I have replaced the map sensor, mass airflow sensor, plugs and wires, cap and rotor, and had the fuel and exhaust systems checked and everything is fine there, and it also has good compression. Despite all these replacements and checks, it still shows the codes, it has no power under load or going up hills, the check engine light flashes when going over 60mph. It also hesitates and will not shift at that speed until I let off the gas. Does anyone know what is wrong/how to fix this? Thanks for any help!