If OP is for sure there are no vacuum leaks, he could test each injector by doing an injector balance test, but I dont know if that's possible with CPI (maybe it is, but that the entire upper plenum has to be taken off - I haven't had a vortec in front of me in like 14 years). If its possible to get to each injector, he might need a scan tool to do it. There may even been an android app for doing the test. If he doesn't have a scan tool, and the injectors can be accessed one by one, a balance tester could be hooked to each one to pulse them and record the drop. But if I remember, that cant be done on the spider without taking the intake off?