Performance dropping as game progresses

[Crisb92]

Hey, I've been playing my current Morrowind game for a fair while now and recently the frame rate in Balmora and Ald-Ruhn has dropped considerably from ~40-60 to less than 20. Also, the game frequently pauses for up to 30 seconds when I'm in those locations. I have amassed a considerable amount of stuff and completed both the Tribunal and Bloodmoon main quests, and am almost finished with the Morrowind one.

 

I have checked with a new game, and there are no problems in either area. My system: Ati 4870, e8400, 4GB. (Haven't had any problems up until now) Save game is at 8.5MB, with a fair few mods and texture replacers.

 

Do you know what is causing this? How can I fix it?

 

Thanks,

Chris.