Seems like the same exact thing happened to me two weeks ago.
I'm thinking it's the timing chain... well, crossing my fingers at least.
Here's my scenario:
Car was idling with the AC on for about 30min while I was sitting in the back seat watching a movie with my son on a laptop with the a sound system plugged in through a power inverter... then, out of nowhere the car dies. I figure the battery died and the car shut off.
About 30min later someone kindly offers to help me jump start it. Nothing, barely turns. I then check all the spark plugs, all good, no water, perfect shape. I check the oil, aslo perfectly clean, no water, nothing, just pure good clean oil. I take the battery out, take it to get checked out and charged. Battery checks out and a quick charge put on it. Try starting, same thing. I then remove the starter, take it to get checked out, and it checks out.
Spark plugs good, battery good, starter good, oil good. Grounds all look good. So, I attempt another jump start. Very slow to turn over, so I let it sit attached to the running car with the jumper cables. Finally, I try starting it, and it starts, but sounds like the belt tensioner is going bad as it's making a lot of racket.
I'm on a road trip, so I figure I'll just jump in and head home immediately... Then, I go down the street for 2miles, now cruising at 60mph, and the car suddenly shuts off (not "slowly dies," but sudden stop). I put it in neutral, and coast to a stop... then, tow it home (4hrs away mind you).
The one thing I haven't tried, is removing all the belts and then trying it. Could be that the AC seized up... but, seriously, could a belt seriously lock up a motor? I would think the belt would just slip until the crank pulley burned a hole through it.
Could it be the timing chain? If the timing chain went, couldn't it lock up the motor?
I really hope the engine didn't seize up... but how is it possible for it to seize up so that it first has trouble, then starts, then seizes again? Seizes again? It's gotta be the chain, is what I keep telling myself.
Please help.
PS. A little background: The car had no issues, No Engine Codes, no Service Engine light, and back in January I did the entire intake manifold and LIM UIM gasket rework. It's a '99 NA 3.8 GT