PROBLEMS WITH GMAX?

Help is sought, please!My system is Dell 4400 P4 1.7 128DDR Ram 64mb GForce 2MXI have found that with all GMAX aircraft that I get a drastic reduction in performance and frame rates after some twenty minutes into the flight. I have used POSKY's CRJ and more recently the excellent Fokker 100. For example, Glasgow to Jersey, 20 mins into the flight, the frame reduces from 18 to 8/9. Selecting views becomes very slow with the aircraft taking longer to 'skin'. Eventually, it almost grinds to a halt! I have cranked everything down on the settings to an acceptable level. I have a large number of AI aircraft and plans. When this is reduced to nil, not much difference. The only way to to resolve this situation is to save the flight, close and then reopen FS2002. BUT the problem does reoccur again some twenty minutes on! I have no problems with the default aircraft. I note through other AVSIM Forums that GMAX does cause problems. Am I alone in this? Can anyone suggest a solution?