200 and not 201 202 203 etc?

Check the injector A and injector B fuses. The only things that can cause 201-08 are an open injector wire, open fuse, shorted injector wire, PCM, open injector, shorted injector. If it runs on all but 7 and 8 then there is no blown fuse. Sounds like someone has been poking the injector terminals with a tester. Splice in two new GM pigtails for those two and recheck.

P0300 is about as useful as the PCM telling you what color the truck is. In the old days the PCM would actually set 301 302 etc.