General Motors sees its post-bankruptcy strategy gain traction in June as a more balanced portfolio of cars and trucks translates into an 11.2% sales increase and gives the auto maker its best month in nearly two years.

However, June’s results also revealed strengthened competition from Asian rivals and the delicate maneuvering the auto maker must make on the truck front as a shutdown to retool assembly plants for next-generation models approaches.

GM delivered 248,750 cars and light trucks in June, compared with 215,358 year-ago, according to WardsAuto data. The month had 27 selling days vs. 26 in like-2011.

The auto maker, which prior to its 2009 bankruptcy relied heavily on pickup and SUV sales, saw car deliveries improve last month, up 7.7% to 106,681 units and roughly 42.9% of its June mix.

GM truck sales climbed 14.1% to 142,069 units, WardsAuto data shows, but pickups and SUVs took just 28.5% of sales in the month, with popular cross/utility vehicles grabbing 24.5% of the mix.

“We’re seeing good car business, but then we’re also seeing some decent truck business,” says Kurt McNeil, GM’s chief sales analyst.

The Chevrolet lineup of the Sonic, Cruze and Malibu passenger cars did the heavy lifting in June, with a combined 57,170 deliveries in a month when nationwide fuel prices continued to soften.

“We’re pleased with the performance,” says Don Johnson, head of Chevrolet sales.

However, Cruze sales arguably reflected evidence of new strength from Asian auto makers devastated last year by Japan’s earthquake and tsunami. GM’s top small car accounted for 18,983 deliveries in June, down 26.6% from year-ago’s 24,896.

Cruze sales have totaled fewer than 20,000 units each month since March.

The Toyota Corolla, by comparison, delivered 25,860 units in June, up 34.8%. The Japanese auto maker witnessed a 54.3% spike in its total June sales with rebuilt inventories.

But Johnson notes GM’s data shows the Cruze boasts both the highest average transaction prices in its segment and the lowest incentives.

GM’s large trucks also felt the sting of competition last month. Silverado and Sierra sales were relatively flat compared with year-ago at a combined 46,045 units. The Ford F-Series, by comparison, delivered 52,117 in the month, up 7.5% on a daily sales rate.

“We’re in somewhat of a transition,” says Alan Batey, head of GM’s U.S. sales and service. “We’ve got a lot of things that are playing out right now.”

GM’s truck inventories were high in June, particularly large pickups at some 135 days’ supply, but the auto maker will begin taking down assembly plants in the coming weeks to retool for the next-generation models.

The scenario limits its marketing aggressiveness, evidenced by a $400 year-over-year decline in incentives on large pickups. “This has played out actually very, very well and in line with our expectations,” Batey says.

Total Chevrolet sales in June rose 10.6%, Cadillac turned in a year’s best 7.5% gain, Buick deliveries grew 22.1% and GMC finished up 10.7%.

The closely watched Chevy Volt extended-range electric vehicle recorded 1,760 sales in June, its second-best month since launching in late 2010.

GM reiterates its industry light-vehicle sales forecast of between 14.0 million and 14.5 million units on an annualized basis.

Summing up the first six months, McNeil says an estimated 4% sales gain bodes well for GM in the year’s second half, when a number of high-volume, new and redesigned products arrive.

“We have some tremendous opportunities in the back half of the year,” he says. “We feel good about where we are and what’s to come.”