Don't use the 5.3 a/c controls from the harness, just wire it into your factory harness. Do you really need the tow/haul switching? Disable it and run one standard setting. You shouldn't need all the BCM stuff from the donor truck. You should be able to disable all the unnecessary stuff and run the bare essentials by programming it out of the PCM. You can disable error codes that would be output to the SES light.