Completed my flex fuel conversion recently. I installed the GM OE sensor and had BB tune it. Install was extremely easy. I started off with a 1/4 to verify operation, and currently have about a 3/4 tank of e85.
The truck already feels so much more responsive. E85 combined with BB ecm and tcm tune is a perfect combo! Total cost of conversion (not including BB AutoCal) was about $75.
Gas mileage is down between 16.5/17, but with e85 at $1.99 and 89oct at $2.35 around me, so it is slightly cheaper to run e85. I would highly recommend it!