So ... I would suggest that you come up with a simple rhythm section with powerchords maybe use the verse section of master. Then you get a metronome and play it over and over again. Do something like 8 repetitions at a certain speed (not your max speed) then turn up the speed a little, do another 8, then faster, then faster, then faster, until you start loosing your timing. Once you've hit that speed take it down again the same way to you first speed. Then go back again.
It's a principle used in many sports to gain stamina, you'll have better results making some type of uphill/downhill drill then constant tempo.
