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Hello, I have some information that should assist you.
Your engine should have multi-port injection, not throttle body. There are a few common problems with this system. One could be the fuel pressure is too low to open the injectors correctly. You will need to check fuel pressure first. The next thing is the fuel pressure regulator could be leaking causing you to lose fuel pump rest pressure, requiring an extended cranking period to build it up. Do you ever have a rough run or black smoke after starting? The third could be the injectors are not opening due to an injector design flaw that has been corrected with a complete replacement injector assembly. There is a TSB that addresses this issue and GM is replacing the injectors under a campaign if they were originally built for sale in California. I believe the campaign will cover the vehicle up to 200,000 miles or 10 years if it was built for California.
Let me know if I can be of any further assistance.