My PS2 Disc Issues

It's not reading discs properly... I can hear it spinning and I've cleaned the lens... I guess the only option left is to take it apart. What's weird though is that it can read PS1 discs, GT4, and Need for Speed Underground 2. It's really strange that other PS2 software won't work. And it also has performance issues, so I really want to fix it. It's lagging in Ridge Racer Revolution, R4, Gran Turismo 2, and Touge MAX. Gran Turismo 2 has slight lag in the midfield. It's particularly bothersome that the lag only happens in the midfield. It's even stranger that it doesn't bother me as much with other PS2 games. What's up with my PS2?