Ok, so when i'm driving the alternator gauge is always steady in the + side, but when i stop the car and bring the rpm to to the same rpm 2000-2500 the gauge is dead even. I don't thinks its the battery(new) because I've used it in a different car and the alt gauge is dead even.

I have a similar problem with my 67 Formula 'S'. I put in a new voltage regulater and it still is always on the plus side of center and boils the battery.

I've known some Barracudas that overcharged in my life, but thats a different story.

Put a manual gauge on it to get a reading to find out if the system is overcharging or the gauge is out of wack.

I would suggest (1)slow charging the batt on a charger overnight & taking it in to your auto parts house & have them load test it to see if a cell is bad but your battery is NEW so not needed. (2) cleaning ALL connections especially the VR ground (3)(most likely) if you have an original type(with the wire wound resistors on the back side of it) VR to get the solid state replacement. thats ALWAYS a good idea & they are only ~ $20 or so.

I bought a new stock appearing voltage regulator with electronic guts at Carlisle, same situation

maybe a defective guage?

If your sure that battery is good that pretty much eliminates all except door #2. My suggestion would be to either clean ALL connections or take a VOM & see exactly where the voltage drop is & clean that connection(s).

Could be a number of things.

You seemed to have eliminated the battery, but for the record, a battery that has sat around with little use undercharged can sulfate and cause this.

It could of course be the regulator

Take a GOOD hard look at the ammeter, with the car off and all loads shut down, and make sure it's not off center

Next is voltage drop in the grounding and wiring harnesses. Nowadays, the firewall / bulkhead connector is a suspect.

Get a digital meter, preferably one with a bar graph underneath the digits, so you can see "analogue" changes, and measure some voltage drops.

Put one proble RIGHT ON the battery negative POST, and the other probe RIGHT ON the regulator mounting base. There should be VERY little reading, the less the better. Anything approaching 1/2 volt or more means you have a grounding problem

Same thing --put one probe RIGHT ON the battery positive post, the other probe on the ign terminal of the regulator. Here again, the lower the reading the better. Anything approaching 1/2 volt means you have a drop in the harness, which goes from the regulator/ igniton--through the firewall connector--to the ign switch connector--through the switch--back out the ign switch connector--through the ammeter--back through the firewall connector--and back to the battery. ANY of these connections can cause a drop, which will cause the regulator to "try" and compensate.

Measure right across the battery terminals with your digital meter. With all loads off, the battery at full charge, warmed up, and the engine at a good fast idle or better yet, "low cruise" the meter should read above 13.5, up to 14.5, and below 15.