The ANT-751 should be a good choice for your location.
I would have tried in the attic also. But the reality for many folks is, the attic may not be a workable reception site. This can be true for a variety of reasons, but generally, the reflective properties of the roof and building materials are to blame. That you're receiving some frequencies is not a guaranty that you will receive all frequencies.
Re. Amplifiers: Reliable reception is not simply a matter of signal strength, rather it's more a matter of signal quality. An amplifier is not able to correct signal quality problems, it's purpose is to overcome signal loss in the cable and splitter connected to the output of the amplifier. Think of it this way, If there is a little bit of mud at the bottom of a shallow hole in the ground, would installing a high pressure pump deliver clean water to the tap? Obviously not. The answer to the problem no doubt lies in digging deeper to access clean water. Only with a supply of clean water would you then consider the need for a pump.
Can you try the antenna outdoors as a test? If you still have trouble outside, with the antenna connected to only one TV (no splitters or amplifiers during the test), then consider adding an FM trap. The FM stations on Cougar Mt. to the NE of you location may be causing trouble with some channels.
http://www.radioshack.com/product/in...uctId=10939219
Several questions;
How many TVs are connected to the ANT-751?
Is there a splitter? If so, how many output ports does it have and are there unused ports on the splitter?
How many feet of coax from the antenna to the TV?
Are there splices or any questionable connections? Any used cable or parts that may have had water intrusion?
Is there any chance cable service and antenna signals are sharing the same coax? (If so, you risk causing harmful interference to licensed radio services. Never mix cable and OTA signals in the same coax.)
Is the tuner set to scan for 'antenna' or 'air' rather than 'cable'?