Motherboard Upgrade question

So I'm about to upgrade my motherboard since I guess my mobo is throttling the crap out of my cpu which in turn leads to other issues. (Fx 9350 on a Asrock 990fx extreme 3).

I have two questions. First, I might go through newegg for it and debating but also worried about their out of box offers, any good luck with those or spend the extra money for new? And my second one is what mobo should I order, I was debating on the Asus Sabertooth 990fx but seen that the cheaper Gigabyte 990fx UD3 has the same gflops as it. I plan on ordering today but have no idea since I'm still new at this.

Never heard of a motherboard throttling a CPU...?

Stay away from open box, you never know what your gonna get.

I have a lost buried somewhere now, the 9370 running at its stock clock and voltage overheats the Vrms.