Re: older gen (1991-older) sportsmobile type vans...who's go
Yes, 6.9 with a Banks Turbo. I've got a C6 with a Gear Vendor overdrive and 4.10 axles. It still runs too tall of RPM in my opinion, even with 33/34" tires. I'd love to have an E4OD (or the ZF5) with the GV for a double OD and keep the 4.10 gears, or go to 3.55's. Funny thing is that the previous owner re-geared to 4.10 only a few thousand miles before I bought it - he used it to tow a travel trailer and wanted the extra gears.
Right now I'm pretty much seeing a lifetime average of about 12 mpg, with highway driving about 13 or so. I was honestly expecting more even from the C6/GV/4.10 combo. I've heard of guys with IDI's with a C6/4.10 (and no OD!) getting 15+. I'm still tinkering with IP timing, and my new IP is barely broken in so I'm hoping to squeeze a bit more economy out of it as I get everything dialed in.
2009 Express AWD, CCV Top & 50-ish home build. Daily driver/camper/kid hauler