I wasn't sure what to title this, but ever since the "black screen of death" incident after EA released their patch for #4, it totally messed up my #3 game. I completely (or so I thought) uninstalled and re-installed the game. Ever since then, all of my saved games are grayed out. At first I thought that they were unplayable, but I accidentally clicked on one of them and it loaded. However, it took an hour to load! After it eventually got to the play mode, it was (and still is) very sluggish. Does anybody here have any solutions or why this would be or what is causing this?

So, while TS3 is a bit dated graphically it's quite intensive, specially on CPU iirc.
How many expansions are you running? And with how much store stuff? How many MB makes your save?
Are you in a notebook or PC? Basic stats like CPU model ( # of threads, base clock, generation) RAM and VRAM and GPU model are needed to know where you stand.
Plus, what mods are you running, if any? Is there any heavy-script mod like Progression, or options like memories, etc...
Lets try ticking off each possibility here.

Ok, for starters, I have all ep's and most of the sp's. I run PC, win 7/64 bit, and tons of RAM, Intel i7 processor. The game ran smoothly until that patch for sims 4 bled over (I'm assuming) to sims 3 through origin. Myself and many others' games stopped working. I uninstalled and re-installed thinking that this would help. It made things worse really. CPU 960 @ 3.20 GHz, 24576 MB RAM, and a GForce GTX 680 vid card w/4095 MB memory. As you can see, I have PLENTY of power to run this game. I also have some of the store worlds although not all of them. As mentioned, the game ran smoothly until I uninstalled and re-installed.

There's no reason a Sims 4 patch should have affected Sims 3. But if you use a third-party antivirus, it might be flagging Sims 3 now, especially if you're playing through the EA App. So try setting exceptions for the game and the App, or just the game if you have a disc or Steam install. You probably know already, but Origin and EA App installs use TS3.exe, while Steam installs and disc installs that don't require Origin use TS3W.exe, with the W.

If that doesn't help, try a clean user folder, and if that doesn't help either, create a new admin account on your computer and try playing there. Your saves and other user content won't be available in the new account, but that's fine for testing purposes. You won't need to reinstall the game.