Yes the driven gears are color coded for the factory workers; They also have the tooth count number marked on them.
A GM dealer, even trucks, may have the old printed parts catalog which gives charts for them. But the older books have tire size listed by type rather than diameters. Like h78-15 etc.
There must still be that info on GM computers at the dealer.
Sometimes a given tire size and ratio will end up to a gear that was never made. In that case, GM used a "speedometer adapter" mini gearbox that fits on the trans. Search ebay for those. The sellers will size it for you.
Also, check your present reading on the highway mile markers. Sometimes the odometer can be Ok but the actual speed reading is wrong. Use a watch to check the actual speed or borrow a GPS that can give speed. Then calculate the error in %, and look on ebay for the matching error correction adapter.