Hyst, if you're using the Slim PS2, lockup issues are usually due to heat buildup - it's not adequately ventilated. I had this problem for a long time, especially with GT4, as it's apparently one of the most intensive discs for the PS2 to attempt to read. I used to go with the q-tip-and-alcohol solution, which worked from time to time, but if your experience is anything like mine, the problem will get worse as time goes on, regardless of cleaning. I ended up buying a small intercooler fan that plugs into the PS2's USB drive for power, and positions a small dust-filtered cage fan right in front of the disc-side vent. It has its own USB drive as well, so you can still use both USB ports. I've not had any more problems except on extremely hot days when the A/C in my apartment can't keep up. When that's the case, I just point a small task fan at the back vent of the processor side of the unit and that seems to help as well. I found it on Ebay - a search for "PS2 fan" ought to turn up something. It wasn't expensive either - $5 or $10 U.S. as I recall. It probably also helps prevent dust buildup by keeping air moving through the casing.
