voltage drops

hi all. Ive got a problem where when driving if i hit say 2500rpm i get a big voltage drop to around 7-8 volts. This only happens while driving. Ive been told this could be an earthing issue but in saying that ive looked over lots of the grounding points and fixed up some dodgey ones. the thing that gets me is when i put a multimeter onto the battery at running time i get about 12.2 volts. From what ive read i should be getting at least 13volts? Is this a case of me just being lazy to detail or could there be something else going on? btw ive replaced the alternator and the coil.

something else you should know is that im running vk efi.
whadya rekon?

This happens every time the motor goes to 2500rpm?, but only while driving.
Where are you measuring the voltage when this happens.... and what with?...not many car voltmeters would be able to show a voltage drop that big. If you are measuring it while on the move with a dash voltmeter it could be a wiring issue/earth connection with where the voltmeter is connected.
Typically a voltage drop of that size results from a massive short, it would have to be through a big cable for it not to burn through. The bonnet isnt touching the top of the battery? If you are getting a massive short all the electrics would be noticeably affected.....ie if the headlights were on they would dim severely.
12.2 volts is not enough with the engine running.....its not enough without the engine running even for a nearly discharged battery. By all accounts you should have a battery that is incapable of starting the car. Should see 13.8-14.5V across the battery at 2000rpm.
You have replaced the alternator and the coil? in an attempt to get rid of the problem? or the problem has just surfaced after replacing these two items. There could be something going on inside the alternator that causes a short at 2500rpm, but never heard of such things happening before