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Don't worry. headers and exhaust are going on right after the limited slip and 3.55./QUOTE]What's your source for 3.55? Most of us get either 3.42 or 3.73.
Are you getting rid of your ABS? Or did you already get rid of it?
 

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If you prefer ABS remain unmolested, choose between 3.42 or 3.73. Here's how:
The 3.73 vs 3.42 Questionnaire
1. This is my toy, not my daily driver?
Y=3.73 ... or ... N=3.42

2. I'm gonna race, or 'play hard' [for money]?
Y=3.73 ... or ... N=3.42
(also see ?#6, unless you are kidding yourself)

3. I'm gonna tow/haul, or 'work hard' [for money]?
Y=3.73 ... or ... N=3.42

4. I care more about city MpG, less about highway MpG?
Y=3.73 ... or ... N=3.42

5. Many or mostly steep &/or very long hills where I usually drive?
Y=3.73 ... or ... N=3.42

6. I've an extra $600 lying around, just in case I NEED to buy and install a new driveshaft?
Y=3.73 ... or ... N=3.42

7. My valvetrain has [AT LEAST] 1.6 roller rockers AND upgraded valvesprings to support a WOT UpShift of at least 6,000RpM or higher (I've also headers)?
Y=3.73 ... or ... N=3.42
(see ?#1 & ?#2)

If 'N'= 7, you prefer 3.08 / 2.93 / 2.563 - why bother asking?
If 'N'= 4 or 5 or 6 then get 3.42 …
If 'Y'= 4 or 5 or 6 then get 3.73 - and maybe a driveshaft upgrade? Maybe not? Who knows?
If 'Y'= 7 then you NEED 4.11 or more, a definite driveshaft upgrade, a torque converter upgrade, headers, heads, cam …

Upgrade the limited slip differential. If you don't have one, definitely get one.
If you upgrade your torque converter, upgrade your external transmission cooler.
 
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It's my way of reframing the following ideas:
3. Every Impala SS & 9C1 should have come with 3.42 or 3.73, buyer's choice.
2. Every B- & D- car that came with 2.93 3.08 or 3.231 should have come with 3.231 or 3.42.
1. Every B-car that came with 2.563 should have come with 3.08 or 3.231.
(0. Every B-car that came with an L99 4.3L V8 should have come with an L35 4.3L V6.)
 

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I'm ignoring the others as I am making a point

You are trying to be more accurate by .00077 for 3.23 but ignore .09272 for 3.73

The gear count called 3.23 is a lot closer to
3.23 than
3.42 count is to 3.42 and
3.73 Count is to 3.73
If trying to be accurate in calculations you typically don't round different figures to different decimal points.

You want three decimals 3.231 you got there from rounding up the 7 from 3.2307
The same applys with 3.73
Round down the 2 in 3.7272

Two decimal 3.73 ?
Then you need to round down your 3.23
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