downtheroad wrote:
You won't win any races and you will be able to watch you gas gauge head toward empty....
Yes, it's a race to see whether you gas gauge or your speedometer reaches zero first! :W
Eastbound I've always found the first big pull out of Golden up to Genesee to be the toughest, partly because it's unrelenting, partly because you're often in a lot traffic at that point. Not as high in elevation as you'll encounter further on up though. The last 1/2 mile or so to the tunnel gets steeper right at the end.
US 6 up Clear Creek Canyon is an alternative, but it's a two lane road with few passing opportunities if you get a line of people behind you.
FWIW, westbound the approach to the Eisenhower tunnel is the toughest. Again, unrelenting, but with a 7% grade at 10000'. The video link posted above by time2roll is from eastbound perspective.