Do you have memories enabled? If so, memories could make your performance suffer.
Do you save any items in build/buy mode, clothes, hair, make-up, textures, etc. that you have edited? These can make performance suffer over time.
Have you played them for a really long time?
Overall, it's sad to say, but it may be time to start a new family in a new world if it's only this couple that is causing problems. The SIms 3 save files are made so that they will continuously grow in file size since every bit of information is saved from birth to death, even their tombstones, for every sim in your game world. This causes eventual slowed performance that can sometimes be delayed by deleting cache and your personal settings (i.e. saved items, hair, textures, etc.), and custom content.
EDIT: I just remembered a mod made by NRAAS that I use called "Overwatch". Do a google search for it. The mod cleans up your game once a game day or immediately at any time you choose by resetting stuck sims, turning off electronics in other households, returning cars, etc.. It has a lot of features that clean up the game that you can enable or disable to improve in-game performance.
The resolution may be the problem. Do you have antialiasing enabled? Your may have to tweak the video settings. Lower the game resolution. Are you using triple buffereing? What are your frames per second (FPS) while your having the problem. If you have AA and triple buffering the video card may not be able to keep up with a lot of changes screen to screen. You might as well enable vertical sync as lcd monitors are locked at 60 hz.
I tried lowering the video settings but it didn't do anything. I have Nraas Overwatch and MasterControler, I tried reset everything and it didn't work I have had AA on low on my old machine and it ran fine, I could have AA on high on my new machine with all EPs and all my sims from the old machine, and it ran beautifully for a few weeks after I got it. I tired Vertical Sync and it gave me no change, I don't have triple buffering enabled either. I don't know what changed to make it run so badly, on some lots it runs at 20-30 FPS and it looks very shuddery. It's almost like my graphics card doesn't want to do a good job playing Sims. I have gotten the card checked twice and each time nothing was wrong. My old computer with a Nvidia 450 GTS and only a duo core processor does a better job running this game then my brand new machine, I only wish I could install ITF on my old machine when it comes out but the disk drive is borken and the wirless adapter is not working either. This is just so upsetting for me ☹️
Did you check yet if your card is properly recognized by the game: http://sims3.crinrict.com/en/2013/06/getting-the-game-to-recognize-your-card.html
I looked and it's not recognized, I tried to do what your site said but it didn't make a change. I could have done it wrong though. Wouldn't it always not have worked if this was the problem? It ran fine before, even with the card not recognized. My old card is listed but not the 660 Ti. A great deal of the geforce cards listed have an M added on, I assume that means laptops?
