Mudbox :: 2011 / 3 Minutes Of Sculpting Then LAG?

I'm scultping a mesh of 1.8 million and everything is fine and smooth. After 3 or 4 minutes the program starts lagging badly to the point it is not usable. If I leave it idle for 10-15 minutes and resume it's fine again, for another 3 minutes. If I close the program and re-open it (as soon as it starts lagging) the lag persists. If I reboot it's fine (for 3 minutes of course).

I've tried changing the graphic's card driver (currently latest nvidia), changing the features in the nvidia control panel to min, and also the ones in mudbox. To be honest I don't think it's the graphic's card fault.

I thought it had something to do with the memory (leakage maybe?), so I did some tests but the working set size is stable at 300K and the virtual memory slowly goes up to 390K where it stops (this during the 3 minutes of sculpting).

I realize with mb 2012 there will be little interest in solving the old version's problems but I reckoned I'd give it a last shot. It's also a student edition so I can't upgrade.Here's my settings

OPERATING SYSTEM
Name: Microsoft Windows 7 Professional
Version: 6.1.7600
Service Pack: 0.0
Architecture: 64-bit
Registered User: Alessandro
Language: 1033
Domain Role: 0
Total Physical Memory: 4026 MB
Total Virtual Memory: 8388607 MB

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