My GPS (a Garmin Montana 610t) will take a waypoint every 50 feet at the smallest increment that can be specified. If you overlay any GPS track on Google Earth where a trail is visible, you will readily see that small twists and turns in the trail are not recorded. GPS distances have this error.
GPS altitudes are not as accurate as lat/long measurements. Garmin has a brief discussion
here. A more detailed discussion is
here.
The elevation difference between the Whitney Summit (14505') and the Portal (8365') is 6140'. The drop from Trail Crest (13600') to the JMT (13482' per Topo!) is 118'.
So, a first pass number for total elevation gain on the round trip is:
6140' + 118' + 118' = 6376'.
I am not remembering any other up hill/down hill sections that come close to the drop from Trail Crest to the JMT. I know that there is a small drop getting into Bighorn, but it wasn't much. So, I think 6376' is a reasonable number. You could call it 6400'. If you want more accuracy than that, a surveying crew would have to measure the entire trail.
