monsoon problems...bad head unit?
Are you still using all original factory speakers?
Part of your problem sounds like someone did a door speaker swap without bi-wiring the speakers as in the stock configuration. In the factory set-up, the tweeters in the door are driven directly by the head unit, while the woofers are driven by the Monsoon amplifier. Note: The amplifier has built in low-pass crossovers, so you only lower frequencies to your door woofers and sail panel speakers. If you have not done any mods to the stock system, then you likely have a problem in the wiring harness. The front channel has output from the HU, as can here bass from the door woofers.
The stock rear hatch speakers are just 4" midranges. Sounds like they are working. SInce they are on the rear channel with the sail panel 'subs' (GM calls them subwoofers, but that's really stretching the meaning of the word), you have output on your rear channel. There is no tweeter on the rear channel in the Camaro Monsoon system. Firebirds have a pair of tweeters next to the 4" mids in the rear hatch.
If you hear nothing from the sail panel speakers, and you've eliminated the possibility of a bad amplifier, the problem is either dead speakers, or bad wiring.

