The thing about final drive ratios is that PCMs are programmed to shift at certain speeds, and the speeds show up incorrectly when you go to a new ratio. If you were to switch from a 2.92 to a 2.93, the speed difference would be negligible and wouldn't call for a retune. If you were to go from a 2.86 to a 2.93, the speed difference wouldn't be negligible, and you may end up shifting at over 6000 RPM if you were not to do a fresh tune on your Bonneville.
There is no such ratio as 2.92 for the 4T65E transmission, so it'* time to change that Wikipedia article! I just searched Wikipedia, but I can only find M15 for the Bonneville under the 4T60E. The 4T60E did have a 2.92 FDR, and it also had 2.84 and 3.06. The 4T65E can be found with 2.93, 2.86, and 3.05 ratios. All the ratios are close like that, so if you find a drive ratio that'* not spoton to the 4T65E as these guys list it but is very, very close, you're probably looking at the ratios of "the other" transmission.
Best of luck, and let us know how it goes!
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94 STEi and 99 SLO
