What happens if you try the test suggested by Hans in the Winegard video? Clip the leads of a 4:1 balun transformer directly to the UHF wires of the antenna, and connect the balun to your coax downlead, avoiding the 8269 cartridge (removed) and the preamp. Do you get UHF signals?
https://www.youtube.com/watch?v=TlQke5QYbng
If you still don't get any UHF channels add a known good preamp.
If you still don't get any UHF try another antenna.