On Saturday, the San Diego club had a back country tour to an antique truck museum and a railroad museum. On the return, several of us made a run up to Mt. Laguna Lodge, elevation approximately 6,000 feet.
Yes, altitude makes a performance difference. One car which was running rich at sea level really loaded up at height and was running pretty rough until coming back down the hill. High altitude air has less oxygen by volume than low altitude air, so with a sea level air/fuel mixture setting, combustion is incomplete in the mountains due to oxygen starvation. So, you will want to lean out your carburetion mixture for the elevation - just remember to readjust when you get back down or you can cause some valve/piston burning.
Another thing to consider is radiator caps. Water boils at a lower temperature at high altitude and the pressure can result in boil over even if you are not overheating. A good cap shouldn't present a problem, but if you haven't had yours checked lately, this is the time to do it or carry a new spare.
Remember what changes you make, 'cuz you'll get to do them again next year for SUNI III at Big Sky, Montana - I understand that's at about 8,000 feet!
"Ole" Olson
P.S. Be careful trying to pass slow moving traffic on the mountain roads - it takes a lot longer (a whole lot longer) than you expect.