12 Second N/A Slant 6?
That's NOT a NAG1.
It's a truck transmission.
The NAG1 is a Mercedes transmission.
It has internal ratios of 1st 3.58, 2nd 2.19, 3rd 1.41, 4th 1:1, 5th .83
It will take 800 crank HP before modification is neccessary. The 1st 3 ratios W/a 3.23 are almost dead nuts equal to a TH400 W/4.56 gears.
The problem is the Mercedes computer. It has to read the ABS sensors on all 4 wheels & be programed for the axle ratio.
The NAG1 is head & shoulders above ANY automatic transmission that comes in an American made car, bar none.