...shortly after the car has been run with the stereo up to about 1/3 voilume.
It only started doing this about 4 days ago.
I am running a Orion 225 HCCA amp, Infinity 120.3SE sub, with 8 guage power wire, and 4 guage ground.
I would have run a larger power wire but the power wire from the amp (there are wires into this amp -not terminals ) is only like 10 guage.
Anyhow, I have a 140 amp alternator, and just put a new Everstart MAXX battery in the car on Monday.
I checked my wiring to be sure there was no pinched/shorted wires and all are looking good.
Anyhow, basically the amp seems to run the sub perfectly fine (nice loud, deep, rolling bass) and then power drops massivly to where the stereo powered 6x9'* are producing more bass and that is absolutely no where near as much as the stock stereo did.
I checked the amp and it is warm, but not hot. I plan on cutting a hole in the amp case and putting a cooling fan over the hole to cool the inside of the amp, but at this point it hasn't really been necessary.

Thanks in advance for any help.

hmm sounds like a complicated problem. i would take your amp to a local audio shop and have them test it. hows your battery gauge...could tell you if you have a voltage drop causing this to happen.

Nope -I have a digital voltage reader visible at all times from the drivers seat -never drops below 14.0 -always stays between 14.0-14.8v -sorry meant to say that in the first post.

I checked my wires again. I am going to try and see if I can change the ground and power wires into the amp -the power is 10G and the ground is only 12G. :?
I hope I can make at least an 8G work.
Took it out for a quick drive and it did the same thing again -full power lasted all of 1-2 blocks from home (short blocks like not even 1/10 of mile each).
I popped the trunk after the power dropped off and looked at the output guage on the side of the amp (it'* basically 3 lights) and whenever it the bass hit or took an ultra low rolling bass the guage would indicate full load output, but hardly sound.

Sounds like you might be crossing some connections. I had a bad connection box in an enclosure once. Anytime i had the signal plugged into the box there, it would play until it hit hard. Wire it up directly to the driver itself, and see what it does.