EDIT: SOLVED. My last driver update install was botched somehow, another update fixed it.

I'm normally able to run Sims 3 with very little lag (even in notoriously laggy towns like Isla Paradiso). When I updated my drivers recently, the game did that thing where it forgot all my preferences (like screen resolution) and I had to put everything back to normal. Whatever, I've done this many, many, many times before. I am confident I did not mess up this step.

But this time, my game didn't recover.

First I had lighting issues. Everything was just.... darker. I couldn't find a fix, other than to run the game in windowed mode (weird?). Annoying, but I could deal...

Then I noticed the lag I was having was not just a "spike", but continual, awful lag. Even turning the camera is an exercise in patience. It's happening in every save, and it's happening in fresh games with no population other than the 3 sims I put in there. It's a headache to watch. It's unplayable. I've cleared caches, and loaded the game without CC (first clearing my .packages out, and then using the "run without custom content" option in the launcher). No dice.

I don't know if the driver update is the culprit, but given the timing, I am suspicious. What can I try to fix this?

1 - Every GPU driver update zaps the Game Options, this is normal. You are certain you didn't accidentally leave things like being logged in or having the TS3 store in-game shopping experience switched on where it might have been off before?

2 - If you are using a third party tool to manage fps capping, chances are that tool will require an update also if one is available to take the new drivers into account. I run into this with RivaTuner (RTSS) all the time, and am on a similar Radeon card currently.

3 - My next inclination would be to roll back the driver update and see if things go back to normal (after once again adjusting the Game Options).

1 - well, that explains it! Now I don't have to wonder why that happens.

I was inspired to check to see if the drivers had another update since the one that messed up TS3. Huzzah, they did. Installing that update fixed all my Sims 3 lagging issues.

I wish I'd figured this out before all the other things I tried. OH WELL.

Thanks for the help, happy simming!