Sometimes when I step on my brakes or if I have my lights on and turn my heater on the battery gauge will drop right down, so much sometimes that it almost wants to stall out.. it has a brand new alternator but I had that the starter and battery tested anyway and they're all fine.. not sure if it'd be a ground or where id even look to find said ground... any ideas would be appreciated

Short to ground, probably in the brake light wiring or switch.

Hmm, I don't know though because it does the same thing when I turn my lights and heat on.. could it be a round in the dash?

. Set idle rpm to specification.

. Clean battery terminal and cable connections. Check the condition of the battery cables, especially the ground cable. Look for unseen corrosion under the insulation. Clean the main ground, where it bolts to the chassis, and apply dielectric grease.

. Remove and fully charge the battery. Most auto parts stores will do this for free.

. Test all under hood and under dash fuses with a test light or multimeter:

https://www.askmehelpdesk.com/cars-t...tml#post252145

Be very thorough, since it could save a lot of time and money.

. Clean the connections of the wire going from the alternator to the under hood fuse box, after disconnecting the negative battery cable.

. Test the battery voltage and the regulated battery voltage, as explained in the link below:

https://www.askmehelpdesk.com/cars-t...ml#post1973613

This work-up should indicate where the problem resides.

Mmm. I think it's a classic hole in brake booster diaphram. Look at the engine vacuum while depressing the brake hard.

Battery alternator and starter were all tested and are good to go.. terminals look clean.. only does it sometimes while pressing brakes.. now does it all the time when I turn headlights and heater on.. checked all wiring in dash and there's no problems there...

Most likely, the battery and/or the alternator are bad. Many rebuilt alternators leave a lot to be desired. Check Alternator FR (Field Response) Signal. Have alternator inspected, if idle speed fluctuates with electrical load, which your's does. The FR signal communicates to the ECM how "hard" the alternator is working to meet the electrical demands of the car, including the battery and any loads which aren't monitored by the ELD (Electrical Load). This square-wave signal varies in pulse width, according to the load on the alternator. The ECM places, approximately, 5 reference volts on the wire. The voltage regulator will drop this signal to approximately 1.2 volts, in proportion to alternator load. The ECM compares the electrical load (ELD) signal with the FR (Charging Rate) signal from the alternator and uses that information to set the idle speed and turn the alternator on and off.

It should not be difficult matter to solve this problem. The steps I gave you should be more than sufficient. If it moves beyond this, the ECM may need to be tested.