Pretty sure 3.91 is the common upgrade for 2016 and later. 3.91 is also the ratio for all the pre 2016 200 series (LX and LC). So the ideal option is to source parts from a pre 2016 that had it's gears updated to 4.30 or 4.88. I think there's some weird stuff that happened at some point for the post 2016 with the axle carriers. But i don't know the details, so more homework would be necessary.So, would the 3rd member from a 4.7 or 4.6L Tundra be a drop in since they used the 9.5" axle? With the 2016+ 8 speed trucks having a factory 3.31 ratio, the 3.91's from the Tundra 4.6L would be pretty mint with a 35" tire, or even a 37. Even with a 37", they would still be slightly shorter overall than the stock 3.31/32" tire combo.
1st gear would be shorter than the 6 speed trucks with 4.88's, but 8th would still be decently tall for the freeway. I figure it would be at 2000 rpm running at 75mph with a 315/70R17