Need help troubleshooting fresh swap

[Jerm83]

Hello everyone , I have been lurking here for a while but this is one of my first posts. I recently swapped a 2005 LQ9 6.0 into my 69 GMC and I recently got it running but it's having issues. I purchased hp tuners pro and I have eliminated the vats and the rear o2 sensors. The engine runs fine when fire started but it will slowly start running worse. If I try to drive it it acts like it's in low power mode but I am not getting a dtc indicating it is. The only thing that strikes me as odd is I do not see any response from the o2 sensors. One came with the swap and the other is new but neither seem to be reading any voltage on the hptuner software. However if I disconnect one of the sensors I get a code for a o2 sensor unplugged. My thought is I should be seeing something from the o2 and since I am not it leads me to believe this is the cause of it running bad. I haven't been able to add a wideband o2 to the system yet to check the a/f ratio. I am still learning all of this software and this is my first ls swap. Any advice would be appreciated.