Sonora Pass with a small trailer & a competent truck?

My trailer is 10 feet (no kidding) from ball to axle! (I just now measured it.) Its dry weight is 2500 lb. -- I usually tow with empty tanks and refill after we are set up in a campsite. My truck has a 6000 pound towing capacity, with a tow package (including transmission cooler). There is no exhaust brake, but in first gear on a steep downhill I have never been able to go faster than ten mph with my foot off the brake.

If I seem super-conservative and risk-averse, that's because I am. ;)