6158 feet in 42 miles is a lot if VERY steep long climbing. The Death Ride in the CA Sierra Nevada mountains is "only" 14,000 feet in 130 miles (to extend that logic, DMD is 19,000 feet in 210 miles). I try to plan my team's hard training rides so the climbing is a factor of ten of the mileage - 7000 feet for 70 miles, 8000 feet for 80 miles, etc. Those are HARD rides.

I'm wondering if there is something funky going on with your altimeter? GPS based altimeters give notoriously high readings. The barometric altimeters are more accurate than the GPS.