just because the schradar valve sprays fuel doesn't mean it's working properly, the spider injectors are pressure sensitive and very picky, if you're not getting enough pressure they just flat out won't open. get a gauge on it and see what you're actually getting. with these spider injectors the difference between a running vehicle and a driveway paperweight can be just a few PSI. grab a gauge and post your numbers for: key on engine off priming peak PSI, how long it holds that peak psi, and cranking psi.
definitely do that before throwing random parts at it. weak fuel pump failures are far far more common cause of no-start issues than sensor failures, especially on these vortec's
also, have you checked for any freeze frames or codes or anything? a sensor failure should throw a code. a fuel pump failure shouldn't.