Re: so slow s1800 9 liter
NC, unless I missed something in the article you referenced, they said that a TH475 with a GearVendors was similar to the current 5 speed Allison backing the 8.1L GM motor. I checked the Gear Vendor site and they mention the usual transmissions (TH350, and some of the electronic 4 speeds). I didn't see anything, unless I missed it, for the bigger AT & MT Allison trans.
I have an AT 545 behind my 8.2L Detroit. If I somehow missed something, let me know.