6.2 Liter in 2500 series

Check the owners manual. Most vehicles built in the last five years can run E85 which is about 78% alcohol or 10% "gasahol" with no modifications. The flexfuel badging is more of a sales gimmick than an actual modification. You will see a decrease in mpg running any alcohol products. The alcohol has less BTUs per gallon than gasoline. So unless your really set on the 6.2 versus the 6.0 you probably dont have a problem.

Actually the Flexfuel badging is not a gimmick- non flex fuel vehicles won't run on flexfuel without turning on just about every lignt on your dash- their computers don't know how to adjust for the alcohol in the fuel, so it turns on the check engine light, the emission lights, etc.- the flexfuel vehicle has the correct computer which can adjust for the amount of alcohol in the gas- it also has hardened stainless steel gas lines, etc. to deal with the fuel- if you don't have that, the fuel lines will rot from the inside out much quicker. You lose about 20% fuel ecomony using flex fuel. The 6.2 is not set to be put in the 2500's- only the Denalis (1500, yukon, and xl) and Max trailer tow pkg.