What settings do you use in the launcher and your Nivida Control Panel? You should be getting 60fps everywhere with latest patch and drivers with your hardware.
Also do you use texture mods and how much vram you have on your card? 1gb? 2gb?
PC specs:
Phenom x4 965 @ 4.0 ghz
GTX 480 1536 mb @800
8 gig 1333 ram
Windows 7 x64
My Nvidia settings are:
AAx2
AFx16
Framelimited to 59
No AO or transparency multisampling
Everything else is default
Game settings: pretty much at ultra with the exception of shadows (high with 4096 resolution and 4500 exterior distance)1920x1080 actor and item view distance settings reduced to half.
Using high res texture pack and a couple of small mods like realistic water and camping lite, but I will note that I did a test reinstall of windows and installed vanilla skyrim which ran at pretty much the same frame rate. Much less video memory used though. I normally use around 1300mb of video memory during play so I don't think it's an issue anyway... I get 59 FPS probably 90% of the time but it drops into the 40's in some city areas and dungeons. For example around the underkeep exit or whatever it's called in Markarth I get about 40 FPS outside that door looking towards the city and some severe lag. Overclocking my CPU Results in large performance increases in Markarth so it's gotta be the CPU, just can't get mine stable over 4.0

The game is still playable and beautiful so I'm not overly concerned about the lag, but it's annoying especially during dungeon combat and I'd appreciate any suggestions. Thanks in advance.