Pulling in a signal with NM=-4.8 dB is tough. I'm amazed that you're pulling in the UHF channels you mention at -20 to -25 dB. Are you getting them reliably, or was it a sample size of n=1 (could have been favorable tropospheric effects)? In either case, these are all 2-edge signals, and folks here will no-doubt tell you you these are tricky beasts to tame. Maybe try walking the roof with your 2476 yagi to see if you can find a Ch-11 hotspot, then plug the DB8e back in and see if you still get your UHF channels there as well. Finally, use a good quality UVSJ to combine them them (i recommend the Antennas Direct one).
Interpreting NM in TVFool reports:
www.aa6g.org/DTV/Reception/tvfool_nm.html