2015 Silverado LV3 4.3l Swap Issues

I picked up a lower mileage 2015 Silverado LV3 4.3l and bought a new Howell EFI harness basic harness. The ECU is from the same model of truck but the not the one the engine was originally running on. The ECU has had VATS, DOD, Flex-Fuel, post CAT O2 disabled in the tune. When I start the engine the idle stumbles bad and starts to run pig rich, but with the MAF unplugged, the idle will stabilize but rpm's will hang if any throttle is applied. With MAF connected (I have two new sensors), the engine creeps towards 100% at idle and the high pressure fuel rail starts to max out. The other oddity is that the 02 sensor seem to read a constant higher voltage with or without the MAF connected (O2 sensors are also new). I see PID's for the heater control circuit for the upstream O2 sensors. I have checked the harness grounds, most of the connectors, and all of the harness fuses seem to be intact. I am using a 3" intake tube with the MAF pipe about 15 inches in front of the throttle body. Thanks for any insight on this.