1998 yukon fuel injectors

The check engine light in on, and we got a code reader it gave code P0307, we have replaced plugs and wires, distributor cap, now someone said check fuel injectors. Where are they, it says it is throttle body injection in the book. Thanks for any help, or a better diagram than our repair manual has

The injectors are under the upper plenum, this is a Vortec system. If you are unfamiliar with this system get a shop manual or have a pro look at it. First confirm proper fuel pressure. 65 psi is required.

Thanks for your help:)