If it is RAM, I have had some success with this test (cheesy to some I know but its worked in some situations):
1) Remember the place in the sim where it crashes - same place every time?
2) Do a soft reboot, play again, crash in the same place?
3) Now do a complete hard boot (unlpug PC power for about 30sec), boot back up and play again, does it now crash in a different area?
If so: likely RAM, try reseating or possibly using a different RAM slot (or remove 1 RAM stick at a time), use test software
Hope that helps out