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Here are the gear ratios for all of the Allison Transmissions that came in the GM 3/4 ton and 1 ton trucks. The 5 and six speed transmission have the same ratios in gears 1-5, if you are doing a 6 speed conversion on your 2001-2005 transmission you will have the same gearing as the 6 speed transmissions for the 2007-2019 trucks.
Allison 1000 & 10L1000 Ratios
| 1st | 2nd | 3rd | 4th | 5th | 6th | 7th | 8th | 9th | 10th | |
| 2001-2005 | 3.094:1 | 1.809:1 | 1.406:1 | 1.00:1 | 0.711:1 | N/A | N/A | N/A | N/A | N/A |
| 2006-2019 | 3.094:1 | 1.809:1 | 1.406:1 | 1.00:1 | 0.711:1 | 0.614:1 | N/A | N/A | N/A | N/A |
| 2020+ | 4.54:1 | 2.87:1 | 2.06:1 | 1.72:1 | 1.48:1 | 1.26:1 | 1.00:1 | 0.85:1 | 0.69:1 | 0.63:1 |