Personally I wouldn't put a 3.73 gear in the car. I would go with a 4.10 gear.
Do not get the diable for a few reasons.
One, it won't fix the speedometer issue. You will need a speedcal for that
Second, Predators normally use too much timing and are too lean. And that's not all of them but a large majority of the time. When you add fuel to correct the situation things like load and timing were way off. This means that they are adding fuel in the base fuel tables. Another clue to this is adding fuel based on RPM ranges. The results to this is a tune that doesn't take CORRECT load and timing into consideration. This results in a dangerous non-adaptive tune
How about the timing tables? The Predator adds global timing, SCT create a complete new table. Why add 3 degrees everywhere when you only need it at say, 5,000 rpm?
Other issues
1. Globally adjusted timing tables.(as previously stated.
2. Glitchy software that sometimes locks up your computer.
3. ZERO technical support.
4. 75% of the adjustments simply do not work.
5. No fine tuning of spark and air fuel.
I would go with a SCT Xcalibrator/Xcal 2. Much better tune than Diablo, you can always modify your own tuners later on after you get more mods, etc.