RayChez,
Well Sir, I see you're heading there from Barstow correct? Well, compared to us, you've don't have the preliminary grade(s) we have to run, even before we get to your area of starting. We live in the San Diego County area and run the 15 to the 395.
But, I made the decision (and posted it on here quite a while ago) to do the entire run, from San Diego to Bishop, starting at midnight exactly. That run, without a doubt, was the best, long distance, non stop run, I've EVER DONE! The primary reason, at that time of night/early-early morning, there was NO ONE ON THE ROAD!!! Talk about a pleasant drive. Besides, if anyone knows that run, from San Diego to Bishop, in that route, they know there's absolutely NOTHING to see or miss, in that entire section.
So, doing it at night, with seriously less (none) traffic, was outstanding.
But, back to your original question. Our rig, an '04 Itasca Horizon, 36GD with the C-7 330 CAT, runs down the road at 32,700 lbs. with a Honda Goldwing hung on the back of the rig and, a 2011 Honda CRV-EXL in tow. Cajon Pass is a pain, but, not all that bad. But, that grade, just outside of Bishop to the north, seems relentless. I think, with the present load, I run it at about 30-35 mph, plus or minus.
The time we did it, around July of '12, the temps on that grade were about 85 if I'm recalling. The temps on the big beast started to do some climbing. I think I may have hit around 207-210 before I topped the grade. There are other grades that have been mentioned but, we survived all of them and the coach did fine.
Now, one thing here, this trip was done BEFORE I found out I had about 30-40% of my CAC and radiator clogged up with all the gunk, oil, debris, and more from the blow by tube etc. I've since removed the radiator and CAC and have done extensive cleaning of the entire system. So, we too are heading up that exact route, to the June lake loop in early July. We'll see how it handles them then. Good luck and, you should be fine, keep the RPMs up to so the engine is at peak HP and the fan is cooling at maximum.
Scott