Hi Thaboomer
It's not just the Lancer that understeers in GT3 - it's a generic problem with all the 4WD vehicles in the game.
The first step towards trying to deal with the problem would be to get a Fully Custom Suspension package as that will give you greater control over the settings for Dampers, Camber and Toe and a wider range of adjustment for the Spring Rates, Stabalisers and Ride Height.
Once you have that you can start dialing in the settings to reduce the Understeer problem you're having (softening the Front Stabaliser, higher Front Camber, Stiffer Rear Damper B etc).
Without a little more detail it's hard to be of more help for now - where are you finding the Understeer to be most obvious, corner entry or exit?