I don't have any idea what mileage you should expect from your Cummins and Allison transmixer in your new-to-you motorhome, but I want to welcome you to at least this forum and at least to the world of the mighty Cummins. How in the world did you escape welcome for two whole days?
I'm also a member at a couple of Cummins forums that would welcome you, too. Send me a PM if you'd like the URLs.
1975 Argosy 28 "Argosy"
1979 Excella 500 31 "Betsy"
1992 Lincoln Mk 7 LSC
2003 Dodge 2500 Cummins "TowHog"
"Lucy Loosehair" the cat - Airstream mascot
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