I have tried finding the code on my rear-end for what gear ratio I have, but it CAN NOT find the casting code anywhere! Im 90 percent sure I have a 3.27 gear option.

If it help its an 87'
Shifts into 2nd at 36 mph at about 5k rpm
shifts into 3rd at 75~ mph at about 5k

 

pull the cover and look. you're wasting your time looking for a code, all that'll tell you is what it left the assembly line with not what it has after 15 years or so.

 

Sounds like your tach reads WAY WAY HIGH.

Only way to know what gears you have is to take off the cover and look.

If you haven't changed the fluid lately, it needs it needs changed anyway. Easiest way to change it is to take off the cover. Look at the gears while you're at it.

 

What do you man it read high. Those numbers are at wot and what mph the shift points are at. Btw the gear oil is brand new.

 

High = reads higher than actual

OK, if your gear oil is new, catch it in a clean can and re-use it.

Only way to know what your gear is, is to look. All else is just a guess. Some guessing methods (tach/mph, count drive shaft turns, "codes", etc.) are less accurate than others; none are really accurate.

 

Is there a place online that converts rpm and mph into a formula to figure gear ratio?

 

yes.
Drumroll please.... It's on this website.
Main tgo page, not the forum, go to equations. That'll get you close enough, but you should be able to find a stamp on the back right axle tube... or on a tag on the pumpkin. If those aren't there, then it's probably not stock so...