Trying to finish a 06 GTO LS2 and 4l65 swap in 59 impala. Using complete e40 ECM and t42 TCM and factory harness. Runs ok but at times goes open loop while driving with a A/F command of 16:1 with noticeable hesitation. Then at times stays in close loop with no hesitation. Stock engine with factory thermostat, runs at 195degress. No codes with seems to be good fuel trims(+5 t0-5). Frist time swapping with e40 ECM but had good results with gen 3 0411 ECM. Any help would be appreciated.