2012 Chevy Express 3500 15 Passenger Van

[gregl]

I have a 2012 Chevy Express 3500 15 passenger van with the 6.0 V8 (flexfuel). I have oversized tires and am considering doing a gear change (stock 3.42 to 4.10). The van was converted to a dually before I got it. Its a fun family hauler but I'd like to fix the speedo issues and put a tune on it that matches the extra wheels and maybe reclaims a few mpg's. I've seen on other threads on here that the Express isn't officially supported but may be able to be tuned. Any advice is appreciated!

[mikel]

can be hit or miss, but they are usually supported