Never a fan of attic installs, lots of things can interrupt the signal. That being said, do you have splitters running in the house? Every 2-way splitter 1/2's the signal strength, maybe by the time the signal gets to your TV, it's just not strong enough for the turner.
I'm up here in Epping NH and pick all those stations with no problem and my distances from the towers are almost the same as you. I do know that my Hauppauge 1600 does a better job of picking up stations than my older LG HDTV, not all tuners are created equal, some better than others.
For my setup I run from my roof antenna (a crappy LAVA HD2805...didn't know better at the time, but does the job) into a 4-way amplifier that feeds 4 devices...this setup works great for me and signal levels are fairly strong on all the TV's & Hauppauge...always trying to minimize use of splitters.