Just pulled out an old Cat download, with a HP-weight -speed on a 6% grade chart.
At 34,000 lbs , RV and toad 330 hp should get you around 45 mph
A 40,000 lbs a 330 hp unit will only do about 38 mph.
Since Cat , went out of the on highway engine market this download is no longer on their web site.
Too bad , JMHO, it was a must read for all DPMH owners.