Certainly he's past his prime, but I'm not sure that's the main driving factor. I don't have home/road splits on pitches for when he was in Coors to know how much that played into it, but there's some really interesting numbers from the past few years.
Tulo typically has murdered the fastball. Since 2009, the years he's had the most trouble have all coincided with fairly large increases in fastball movement he's faced, with this year having by far the most vertical AND horizontal movement yet. Similarly with the slider, there's also a sharp change in movement this year, and Tulo's numbers versus it have dropped drastically. I haven't dived into it far enough to do a proper analysis, but I did find it really interesting.