General Motors increased North American production less than 1% in May from like-2012, based on a WardsAuto estimate.

Due to GM’s decision to discontinue reporting monthly production data for its North American plants, WardsAuto will estimate the auto maker’s output by plant, platform and vehicle line beginning with May’s results. Estimates will be accurate and based on reliable resources available to WardsAuto.

GM’s gain pales in comparison to the overall 5.9% year-over-year uptick for all North American light-vehicle manufacturers.

Slower output at the auto maker’s Fairfax, KS, plant, where the Chevrolet Malibu and Buick LaCrosse are assembled, can be blamed in part for the tepid results. Production at the Orion, MI, facility (Chevrolet Sonic, Buick Verano) also was off from year-ago.

Other contributing factors to the lukewarm results include the Bowling Green, KY, plant, closed since March for re-tooling to the all-new Chevrolet Corvette launching in July, and the Oshawa, ON, Canada, No.2 plant, which is winding down output of the ’13-model Chevrolet Impala. The redesigned ’14 Impala is being built at the Oshawa No.1 and Hamtramck, MI, facilities.

Also, a year ago the auto maker was still building small pickups at its Shreveport, LA, operation, which closed in August.

On the plus side, production at the Silao, Mexico, facility, which just launched re-engineered versions of the Chevrolet Silverado and GMC Sierra large pickups, was up 61.4% from year-ago, when the plant was down part of the month in early retooling for the new trucks. However, Silao’s production of 20,126 units in May indicates it has had a smooth ramp-up for the new models, launched in April.

Two other plants build the Silverado and Sierra. Fort Wayne, IN, begins production of the new models in July, and Flint, MI, launches ’14 output in January. Those facilities also underwent preliminary tooling for the re-engineered models at various times last year.

GM surged ahead with production of large SUVs at its Arlington, TX, plant where volume was up 8.2% in May from year-ago. The operation, which added a third shift earlier this year, builds the SUVs off the same GMT900 platform as the Silverado/Sierra. Arlington begins production of re-engineered versions of those vehicles in first-quarter 2014.

Production remained strong for GM cross/utility vehicles, as well. The Chevrolet Equinox and GMC Terrain combined for a 9.1% increase at the Ingersoll, ON, plant, and output of GM’s large Lambda-based CUVs rose 6.3% at the Delta Township, MI, facility.

Production of the Cadillac ATS spurred a 41% increase at the Lansing Grand River, MI, plant.

GM output is forecast to decline 7.8% in June from like-2012 to 266,000 units, in part due to the Fort Wayne plant readying for its July changeover to the ’14-model Silverado and Sierra.