U.S. retail heavy-duty truck sales totaled 17,776 in April, the highest level thus far in 2014 and 13.6% above the same month a year earlier, WardsAuto.com reported.

April also marked the eighth consecutive month of year-over-year growth and was 8% higher than the March total of 16,452.

Last month’s tally was the highest since 19,695 big trucks were sold in December, typically the busiest month of the year. Four-month cumulative sales were 62,323 units, a 14.5% increase overlast year’s pace.

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