2000 GMC DENALI Engine And Engine Coolingengine Problems

I'VE EXPERIENCED A VERY SERIOUS/DANGEROUS PROBLEM ON 9/5/03, 11/1/03, 11/2/03 & 4/18/04: THE ENGINE HAS COMPLETELY SHUT DOWN WHILE I WAS DRIVING MY SUV. THIS HAS HAPPENED WHILE I'VE BEEN DRIVING ON HWY, ON BRIDGES/ TUNNELS (WITHH NO SHOULDERS), & WHEN I'VE STOPPED THE SUV @ TRAFFIC LIGHTS & STOP SIGNS. THE COMMON DENOMINATORS FOR THE ENGINE SHUTTING DOWN SEEM TO BE: (1)LONG DISTANCE TRAVEL-ON ALL 4 OCCASIONS I HAD BEEN DRIVING THE VEHICLE ON THE HWY FOR 100 OR MORE MILES @ SPEEDS OF 60-70 MPH BEFORE THE ENGINE WOULD BEGIN SHUTTING DOWN (2)WEATHER- ON ALL 4 OCCASIONS, THE TEMPERATURE WAS 75-85 DEGREES WHEN THE ENGINE WOULD BEGIN SHUTTING DOWN WHAT TYPICALLY HAPPENS WHEN THE ENGINE SHUTS DOWN: WHILE ACTIVELY DEPRESSING THE ACCELERATOR PEDAL, I WOULD SUDDENLY NOTICE THAT I WAS NO LONGER GETTING ANY ACCELERATION POWER I WOULD THEN BEGIN TO PUMP THE ACCELERATOR PEDAL TO NO AVAIL...