U.S. retail heavy-duty truck sales continued their torrid pace, topping 20,000 in September for just the second time since 2006, WardsAuto.com reported.

The September total of 20,078 was 24.5% above a year ago and the highest since December 2011. It was also the first non-December month to see sales above 20,000 since November 2006.

The increase marked the fourth straight month in which year-over-year gains have topped 20%. Similarly, medium-duty truck sales leaped 35.5%, the biggest jump in three years, led by a surge in Class 7.

All major original equipment manufacturers reported gains in their heavy-duty sales, with three of six major brands topping 30% year-over-year growth.

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