Boat wouldn't come on plane

So this past weekend I took the boat up to Boca Stampede reservoir near Reno NV. I had 6 people in the boat and the ballast tanks full and it would not come on plane for some reason. I understand altitude could be an issue, because it is 7,200ft. But is there anything anyone else thinks could be the issue? Even when I emptied the ballast tanks it still wouldn't come up on plane. It was an intermittent problem too, because sometimes it would accelerate and other times it wouldn't. I'm wondering if it's the altitude, transmission, or what? It has never done this before and doesn't do it here in the local lakes or rivers. Any suggestions or help would be great