Are you gaming on a single 1080p monitor? If so you should return that 780 ti, buy a 780 and get a better processor with the extra 200$, because a 780 already crushes everything at that resolution.
The card was actually an Xmas gift, can't return it. It's okay, I'll get a new CPU, got a budget of $300, any suggestions?
I see, that's understandable and a nice gift to be given! If you buy a new processor you are more than likely going to need a new Mobo as well especially if you are going with Intel (recommended) because they are not compatible with AMDs AM3 socket (which is what you currently have).
300$ is going to be cutting it a little short though as you will probably need more like 400$ unless you really cheap out on the mobo.
I'll get the cash, just recommend me what mobo and PCU to buy.
If you're just looking at wanting to max out games and you don't really care about things like video editing or rendering or having that extra compute power these two will do you fine at about 400$:
If you do want to have that higher computing power for stuff like rendering this CPU would be a better call: