Yea the premium delco radios had limiters in them because they had more powerful amps in them. This would be an example of the premium radio, it'* what'* in my '87.
I noticed that with this radio, the volume would go down if the bass hit hard, but when it did hit it sounded GREAT. But just for kicks i tried another delco radio i had laying around, just a plain old one, and it didn't have the limiting in it. It also sounded like total crap when turned up, where as the premium unit kept a decent sound even at MAX. As you can see in the picture i only have it about half volume, and that'* where the limiting started to come in. So as far as i see it, just leave well enough alone until you can get an aftermarket radio.
And on a side note... is it sad that the radio in the picture sounds better than my pioneer unit i had before? Lol