Here's a possibility for you if you want to test the injectors. I while back I got annoyed with the lack of a standard pressure test port on the Toyota fuel rail, so I made a few of these:
Haven't tried one out yet, but it's simple enough it should work. It replaces the OEM banjo bolt (on the right) for the hard line that goes to the cold start valve with a new one that has the standard Chevy test fitting. With this I can use my Kent-Moore to do an injector balance test without pulling the rail and injectors out.
So if you want to come by my shop it shouldn't take more than 15 minutes to install one of these and test the injectors. If they test OK and the EGR isn't leaking, I'd say go ahead and drop the cabbage on new O2 sensors.