Another update :

i swapped out the uno for a less powerful Rockford ( punch 1000x2 ) and the issue completely disappeared.
I now have my upper bass frequencies back, it sounds much better and 80hz is solid again.
On the hunt now for a more powerful amp than the little RF ( heating up, doesn't like being bridged @ 3 ohm ).

Does anyone know what would cause an amp to fail in the upper bass registers ?
Always in the 80hz area, if 80 was eq'd almost completely down and the nearest bands turned down a few
db's the issue mostly vanished. The uno failed only in this area. It was fine before the box fell apart.
I removed the lid hoping to find a blown cap or diode or ? , but all looks well. Maybe an IC somewhere failed ?

happy to finally have this diagnosed, it was irritating as hell.