The Mitsubishi GTO is not mandatory...I've won the Clubman Cup in much lesser cars (even front-wheel drives). The problem is you've gone from one of the simplest cars in the game to one of the most
complex. There are a bunch of cars in between to experiment with. I remember I started in a '88 Nissan Silvia Q's for awhile, then at some point I jumped in a Camaro. And I could barely drive the thing! ...till I switched my dual-shock controller around as written below. After that my game improved dramatically. I eventually went from a Camaro to the Subaru SVX...to a Civic...Supra, finally a Viper...
Anyways, Gt is a game of skill (as you're finding out). It's not an arcade racer in which you can just jump in and start being a demon--it takes actual
work
May I offer you this piece of advice? What helped me early on was to
1. Go in the options screen
2. change the configuration of your dual-shock (assuming you have a dual-shock) so that gas and brakes are now on your
right analog stick. This way you can get variable amounts of gas/brakes. ]
Right now I bet you're using X and [] right? This is akin to being in a real car and flooring the gas every time you push the accelerator, then stomping on the brakes full-force every time you need to stop.
Other than this, I also advise you do the
license tests for awhile till you can at least get silvers semi-reliably. Also,
drive around the tracks in Time Trial mode (arcade section). Keep driving around each track till you get to
know it. Knowledge of the tracks (where to brake, where to apex, where to accelerate etc) is extremely important--way more important than horsepower. Make it a game against yourself and keep driving on an empty course till your lap times begin to fall.
HTH