I got the slim PS2 at about the same time, and GT4 plays great. I'd try your other games, plus some DVDs, and see if anything else has a problem. Make sure it's not something simple like fingerprints ...
IIRC, you can soft mod your xbox for XBMC so you don't have to go the mod chip route unless you want to.
Some results have been hidden because they may be inaccessible to you
Show inaccessible results
Feedback