2008 chevy tahoe flex fuel?

[CRHIS G-UNIT!]

ok so we have a 2008 chevy tahoe with the 5.3 liter vortec flex fuel engine in it. Before we left the dealer with it they sales man told us that we could only fill the tahoe up with a quarter of a tank of e85 so if it was a quarter filled we could only fill it up to half a tank...is this true? can you only use a certain amount of e85 with the flex fuel tahoe? or can we fill it up all the way?

any comments & suggestions will be appreciated