4 hours doesn't sound like molly. That sounds like methylone. A half a gram of MDMA should have you rolling at least 6 hours.
Test your stuff if you can.
As for your doses, 250mg in a night is all that you should really need if you have clean MDMA. Anything more than that is a waste and causes a nastier crash. Once your brain runs out of serotonin, you can't go any further. About 1 1/2 to 2 hours after your first drop, anything after that is all wasted and just adds to the crash.
As for the elevation, as everyone else has said, it shouldn't make a difference. Just be aware that the air is thinner at the higher elevations so adjust your physical exertion when you're rolling to make sure you get adequate oxygen.