I wonder if the HD tuner you have mightn't have the best of receiver sensitivities ?

The two local HD (1080i) stations here are loud and clear with no amplification, using what is essentially a coat-hanger mounted 40' off the ground, with good RG-6 coax from there to the tuners (HDHomeRun).

Now our more distant 3rd HD station is just not reliable enough (about 80 miles away, I think), despite my best efforts thus far with exotic antennas and amps. But their analog counterpart is now nearly crystal clear 100% of the time with the new setups.

Cheers