From Cody to the east entrance is a gradual climb. Once through the entrance the grade increases to something like 7-8% for about 7 miles to Sylvan Pass then descends with shallow grade to the elevation of Yellowstone Lake. The road stays essentially at lake level to West Thumb Junction. Some minor ups and downs to Lewis lake then down with some 6-7% grades to the South entrance. From there one final up and down with 6% grades to Jackson Lake.
I doubt that you will have any traffic problems getting to Colter Bay. We left Grand Teton on July 2nd in 2012 and had no such issues driving through the Parks to Cody. In our experience, there is more traffic and animal jams on the western side of the lower loop.
We always leave the area before the 4th of July to avoid the crowds, so your experience may vary.
