what exactly is it doing? is the tach not working when it dies? can you hear the fuel pump whine? is it stumbling?

CEL on?

its not a "main relay"-GM's dont use that style. they use a fuel pump relay, but not a main injection one like most imports do.

i can give you some info for the GM dealer we have warranty work done with if you would like, and get him an appt. if you would like.