Allison man; "I have another project" I currently have a argosy motorhome with a 454 and th400 and 4:10 diff. I have a AT545 with a chevy adaptor. When we looked at the gear ratio of the first gear in the allison it is so low that if I installed 321 gears instead of the 410 I have now I would still have a lower first gear than I have now with the th400. My thought was to end up with an overdrive out of the deal. Let me know what you think.