This is my fantasy team, should I trade Gore for Brady or Gore for Mathews and Colston, or keep Gore?

Yea, the people in your league messed up. There's no way Gore should have fell to you at your second pick, in any format, even in an 8-team league. The Mathews and Colston deal is a little interesting but your top WRs are really good anyway... you'll find someone better than Berrian off the waivers in due time. Keep Gore and reap the benefits.