New build won't stay running
 

Hey guys. I've got a fresh built 5.3 with a 600 lift cam. The motor ran great through the break in process. I let it idle for about 45 minutes. I then shut it off and about 15 minutes later went out to fire it again. It started and then died immediately. I know I have to go get it tuned but do you guys have any other idea of why it is doing this? It's an 02 Tahoe Z71. Thanks for any help.