I had my original TH125C swapped out for a 4T60. While I love the lower rpms, it is a bit of a dog now with the stock 1988 GT 2.8L.
The ID on the trans was completely wash away. So that make identification a little tough.
to calculate what it might be it looks to be a 2.84.
My rpms at 70mph are approx 1870 and I have the stock size tires...diameter 25 1/4". I verified the rpms by usin my scan tool hooked to the ALDL and monitored it in live mode.
My highway mileage is 27mpg, which I love, but the acceleration at highway speeds is what annoys me.
Living in Arizona, we have mountains everywhere and the uphill climbs are a bit of a challenge.
What is the complexity of changing the final drive ratio on my 4T60 / TH440? Are there any great how-to articles?
I still have the original TH125C and axels if anything from it could be used in teh 4T60. I know they are completely different beasts, but GM does like to use as many parts across the different models to keep costs down.