After months of stellar gains, sales of medium- and heavy-duty trucks in the U.S. fell back to Earth in November, WardsAuto data shows.

While deliveries increased 39.1% from like-2010, they paled in comparison with October’s soaring 62.8% sales rate, the biggest year-on-year jump in 2011.

Lesser gains in medium-duty classes tempered a 70% spike in November’s Class 8 sales, compared with like-2010.

All Class 8 manufacturers saw increases, from the 112.4% surge by PACCAR’s Peterbilt brand, to the 14.8% hike by Daimler’s Western Star.

The entire medium-duty sector ticked up 5.4% compared with year-ago, as classes 4 and 7 each slipped 4.0% and classes 5 and 6 recorded modest increases.

A 137.9% boost in low-volume, import-model sales, largely fueled by UD Trucks, up 144%, wasn’t enough to offset a 5.0% drop in Class 7’s domestic deliveries.

International’s 25.2% decline to 1,039 units was the segment’s largest shortfall. International ceded the volume-leader slot to Daimler’s 1,220-unit total in November.

Class 6 sales rose 13.8% as sales of domestically built models rose and imports fell. Imported Mitsubishi Fuso models suffered a 76.0% plunge from like-2010. Peterbilt’s 111.2% groundswell was the benchmark performance in Class 6.

Class 5’s 11.6% sales increase was led by International, up 131.7% compared with prior-year. Volume-leader Ford saw deliveries climb 33.8% in November, giving the Blue Oval a commanding 69.5% market share, up from 58.0% year-ago.

Class 4’s 4.0% drop largely was due to declines of domestically built models, specifically at Ford and International. Each saw its sales plunge more than 83%.

Isuzu bucked the trend, recording 120 deliveries for a 448.6% gain in domestic-model sales.

Through November, U.S. sales of big trucks were pacing 40% ahead of year-ago, with 272,879 deliveries.

Class 8 inventory rose to 34,123 units in November, compared with prior-year. But days’ supply fell to 50.

November 2010 saw 22,259 in inventory, for a days’ supply of 56.

Medium-duty trucks numbered 36,463 in November for a 94 days’ supply. Prior-year’s stock totaled 24,627, or 67 days.

cschweinsberg@wardsauto.com