The rollout of GM's redesigned full-size SUVs and low incentive spending in the latter part of the year boosted average transaction prices. Incentives fell 6.9 percent from a year earlier, and GM's average transaction price rose 6 percent, according to TrueCar.
"They got the double hit of better volume and better pricing than most others," Jominy said.
"They had a blockbuster Q4 that we could see coming from a long way out."
Now, with the microchip shortage squeezing output, GM executives said it had less than a five-day supply of some top-selling vehicles, including the Cadillac Escalade and the GMC Sierra heavy-duty pickup.
The automaker last week extended downtime at three assembly plants because of the chip shortage until at least mid-March and said it will delay shipping vehicles at two others. GM plans to divert its chip supplies to plants that build full-size SUVs and pickups to keep them running at full capacity.
GM said it expects $10 billion to $11 billion in adjusted earnings before taxes in 2021, even after a $1.5 billion to $2 billion hit from the chip shortage.
The automaker gained half a point of U.S. share last year to end 2020 with 17.3 percent of the market. Its share was 18.3 percent in the fourth quarter, a three-year high.
"When everyone doesn't have inventory, it was easier to do better," Jominy said. "Everyone had fewer incentives. Transaction prices are through the roof, and consumers are buying up everything they can."
Duncan Aldred, vice president of global Buick-GMC, told Automotive News last week that his brands are unlikely to reach pre-COVID-19 or pre-strike inventory levels this year, but he still expects to grow market share and profitability.
Many dealers are now getting buyers lined up even before vehicles arrive on the lot, Aldred said.
"That's just a win-win for everybody," he said. "The stock turns quickly, the dealer can make more money and the customer is getting a fresh vehicle."