BIRMINGHAM, Mich. - General Motors Corp. will test the market for a full-size luxury hybrid SUV when it releases the industry's first vehicle in that category — the Cadillac Escalade Hybrid — next month.

It's a market that could be hostile. U.S. sales of the non-hybrid Escalade have fallen 29 percent so far this year as consumers spooked by high gas prices and the shaky economy abandon larger vehicles.

Sales of GM's other hybrid sport utility vehicles, the Chevrolet Tahoe and GMC Yukon, also have been slower than GM had hoped for. Through July, hybrids have made up 4 percent of total Tahoe and Yukon sales, fewer than the 5 to 6 percent GM predicted when the vehicles went on sale early this year.