INDIANAPOLIS (AP) â¿¿ Allison Transmission Holdings Inc. said Tuesday its fourth-quarter net income tumbled 75 percent, pulled down by expenses related to a new labor contract and lower demand from the North American natural gas industry. The Indianapolis-based company, which makes automatic transmissions for commercial, military and transit vehicles, earned $11.2 million, or 6 cents per share, in the last three months of 2012. That was down from $44.5 million, or 24 cents per share, in the same quarter in 2011. Allison said the recent quarter's results included $7 million in costs related to a new labor agreement and a $9 million product warranty charge. Excluding those and other one-time items, the company posted an adjusted profit of $46 million for the recent quarter, but didn't say how much it earned per share. Revenue fell 6 percent to $487 million from $516.1 million. Analysts, on average, expected adjusted net income of $45.7 million, on $440.3 million in revenue, according to FactSet. Allison said its on-highway sales, which include transmissions for busses, motorhomes and other vehicles, rose 7 percent to $188 million. But North American off-highway sales plunged 76 percent to $17 million, hurt by lower demand for equipment used in hydraulic fracturing stemming from a drop in natural gas prices. Off-highway sales outside of North American jumped 58 percent to $30 million, on strong demand from energy and mining companies, the company said. For the full year 2012, Allison earned $514.2 million, or $2.76 per share, up from $103 million, or 56 cents per share, in 2011. Revenue fell to $2.14 billion from $2.16 billion. The company said it expects its 2013 sales to fall between 6 percent and 8 percent from 2012 levels, citing continued uncertainty in many of the markets it serves. Based on the company's 2012 results, the guidance implies 2013 revenue of between $1.97 billion and $2.01 billion.