You have fire, your fuel pump is running. Have you put a fuel pressure tester on the fuel rail & checked fuel pressure? I believe key on prime pressure on a ls1 engine should be around 56 psi.
Also you need to pull the fuel rail up & check to see if fuel injectors are opening. Have assistant crank engine while you check for spray from injectors. Have a fire extinguisher at hand & catch cans under the injectors.
Have you checked for codes with an obd 2 scanner? I ask because there are codes that don't light the ses, but can keep your engine from running.
How about your security light. When you turn key to on, the security light should come on. Then go out after several seconds. If security light comes on & stays on, fuel injectors are disabled. If security light doesn't come on at all, you need to fix that.
To help you troubleshoot, here's a link to the 99 service manual. Be advised that GM changed the format of 96 & newer service manuals. It's harder to find what your looking for, but not impossible.
www.mediafire.com/?40mfgeoe4ctti