I downloaded the most recent (as of 3/5/23) Killer drivers Killer-PCIe-Ethernet-Controller-Driver_RWTJJ_WIN_33.22.1182_A50.exe and when I ran it I got 3 choices: modify, repair, remove. I chose the remove and after it finished there was a restart and voila DL and UL speeds were at or above my ISP plan! Yay. The driver was 9.0.0.50 and there was no Killer Performance software. I did set a restore point.
The Remove option worked for me, after trying for months and getting advice elsewhere.
Was getting 300 down, 2 up for months; now I'm back up to 307.89 down, 236.01 up.
One thing to note: after I chose the remove option and ran the installation routine, I did get an error prompt saying it had NOT completed correctly. That concerned me, but I decided to just reboot anyway.
Thanks so much StephenRudolph!