Engines don't go as fast or get as good a gas mileage until they're broken in. I wouldn't worry too much, since that's not a top speed sled anyways, could have high altitude clutching and gearing though.
I have had a 2007 and a 2009 MTX if you did not have the dealer reclutch or regear that speed is about right. I only reclutched mine and top speed was about 75 mph.