Engine dies at highway cruising speeds

2003 Suburban 1500: engine died at cruising speed ( 65-70 mph) twice in last week (June 2009). Coasted to off-ramp ( I was on Interstate hwy)
and on to feeder road, put the car in park and it started fine and drove
home (35 miles) with no more problems. Next day, problem occurred
again, only this time it took several cranking cycles to start. Both times
the temperature here in Houston was extremely hot (100-102 degrees)
and the car had been driven at least 30 minutes in each case. No check-engine warning lights appeared.

My first conclusion was that it was an ignition problem, since the engine quit instantly.If it had been a fuel problem( vapor lock, for exam-
le), I would think the engine would have died more slowly due to resi-
dual fuel in the lines. Before I start my diagnostics, I would like to know
if someone has had a similar problem, and could offer suggestions.

Thanks,
Milton Gerdes in Houston,TX