when a a/m tank is installed it comes with a matching pickup tube (sender is usually attached to this tube at the time of installation) however if the installer is not very conteiensious they will skip the seemingly unimportant & time consuning task of this tube change over & you will have a high capacity tank but cannot use the extra capacity! if this is youre case then you simply need to contact the mfg of the tank and I am sure they will send you a tube & the dealer should install it as it was not correct at the time of sale, as far as the gauge goes I belive there is a procedure for recalabrating the tank sender to read the increased capacity witch also corrects the DTE function, however I cannot find it (not where I thought it was) Blackhat will probably remember it>