I picked up a Giant ATX a while back for small change and spent some more on it at the local bike shop getting it road worthy. I had intentions of riding to work on it but tried it once and nearly died (due to lack of fitness, not the bikes fault !). It has sat ever since, with me saying to myself 'I will get riding that again one day.....'
Actually, it just might be the bike. At least a little bit.
There is a world of difference between my mid 90s Schwinn Hurricane (a mountain bike, built back when Schwinn was its own company and still made bikes in the US) and my Specialized Crosstrail Disc. I've done 30 miles on the Crosstrail with no problem. A summer or two ago, I rode the old Schwinn up to the store about three miles away, and back...and I was more sore and tired having traveled 6 miles on the Schwinn than doing 30 miles on the Crosstrail! Better (and more suitable) tires, a lighter frame, more efficient ratios, more comfortable riding position, etc., make a noticeable difference.
My better half noticed differences when I upgraded the bikes. She was using a Giant Sedona, with the knobby "street" tires (it has a ridge down the center to assist, rather poorly, on paved streets). I upgraded those to Vittoria Street Runner tires (26 x 1.6) and she noticed the change. I finally upgraded her to a Specialized Roll last summer--it has 2.3-inch wide tires on it, and surprisingly even at their lower pressure rating, that bike is even easier to pedal than the Giant with the Vittoria tires. Not only that, the riding position is way more comfortable.
It's just a matter of using the correct type of bicycle. I see so many local riders struggling on paved trails and streets on a mountain bike, which they buy more for status and appearance rather than practicality. It took two bike shops to talk me out of a mountain bike (the Hard Rock or the Rockhopper) into the Crosstrail...and no regrets so far.
The Epic road bike will be more suitable for paved streets than the Giant ATX (which should be great on dirt trails). If everything is set up correctly, hopefully you'll find the Epic an easier ride on pavement than the ATX.