Mine did this Chek out the fuel pump resistor. Next time it does this try this trick. Its bypassing it on the relay. Worked for me. If it cures it then you know what it is. 50 dollar part on GMpartsdirect.com and looks insanley easy to change I havent changed mine yet I just did the bypass. Heres a link to check out just bend the tab on the shown relay.

L67-equipped cars: My car starts and then stalls. Repair inside..