DETROIT (Reuters) - General Motors Co (>> General Motors Company) again boosted discounts on its full-size Chevrolet Silverado pickups after being outsold in March by Chrysler's (>> Fiat SpA) Ram 1500.

On its consumer website, Chevrolet on Thursday was offering discounts of up to $8,162 on the light-duty Silverado 1500 and up to $8,974 on the heavy-duty Silverado 2500HD.

Some dealer discounts around the United States were even higher -- up to around $10,000 -- on the Silverado and its sister model, the GMC Sierra, as many dealerships added their own cash to official factory offers.

Heavier spending on the big trucks is likely to cut into profits at all three U.S. manufacturers, although full-size pickups remain among the most profitable vehicles in the industry, accounting for more than two-thirds of the U.S. automakers' global pre-tax earnings.

GM had hoped to begin winding down rebates and other incentives on its full-size Silverado, whose sales rose 7 percent last month to 42,246, still well behind segment leader Ford Motor Co's (>> Ford Motor Company) F-Series, with sales of 70,940, up 5 percent. Ram sales jumped 26 percent, to 42,532, driven by aggressive discounts of up to around $8,000.

Chevy and GMC dealers have turned up the discount blowtorch in early April, carrying over and fattening offers from March.

On its website, Courtesy Chevrolet of Phoenix on Thursday was advertising a 2014 Silverado 2500HD Crew Cab for $44,669, a $10,066 discount off the sticker price.

Bob Bell Chevrolet in Baltimore was running an Internet special on a 2014 Silverado 1500 Crew Cab for $36,743, a $10,382 discount.

In Utah, Salt Lake Valley Buick GMC advertised a 2014 GMC Sierra Double Cab for $37,328, a discount of $8,397.

(Reporting by Paul Lienert in Detroit; Editing by Leslie Adler)

Stocks treated in this article : Ford Motor Company, Fiat SpA, General Motors Company