i run that hill with about 16,000 lbs and i usually do 45 to 55 depending on time of year(egt's)
usually average to dumont and back 11.5 mpg approx. get guages ( egt's,boost) so you dont melt your motor.
took my about 30 gal there and back this time(wow) usually can do it with 20gal.
Capt