Hey so I have one lot that is pretty large and has a lot of different high graphics objects on there, as well as some CC. The problem that I've experienced is that when I try to play this lot and select ultra speed or fast speed, both run at the exact same speed as normal speed. The only difference is that the in ultra speed and fast speed, the audio seems to speed up. I initially thought that this problem was due to CC so I temporarily removed all CC from the game only to discover that not to be the problem. However, on a whim I decided to give up all six pets on the lot up for adoption. Once the pets were removed from the family, ultra speed and fast speed began working again. When I tried moving just one pet back in, slow down occurred. Any fixes for this? Because I'd really like to be able to have pets on the lot.

You're purely working with the limitations of your computer's processor and/or graphics card.

Things that cause lag include large lots, large families, large structures, lots of decor and/or landscaping, mirrors, fountains (and other items that include animations of any kind), and CC objects with higher poly counts than default items generally have. (CC is not inherently lag-causing just for being CC. Poly count is the issue.) Obviously, the more of those factors that are in play with a particular lot, the more potential for lag and other issues.

So, the only "fix" is to play smaller, less heavily populated, less decorated, etc. lots. What's acceptable depends on players' computer specs and individual tolerance levels.

One thing you might consider, with this particular lot, is resizing it with Mootilda's LotAdjuster, and to simplify it, where possible, by removing some stuff. Turning off shadows and mirror reflections can help too.