Hi, looks like a creative team! I think you could replace either gyarados or slowbro because they're basically the same type and add weaknesses to your team. I might try Cresselia over slowbro because it can serve as a backup TR user, can use Skill Swap and give good psychic coverage. also, I might try a fire type on your team to make a nice FWG core of Gyarados, Amoonguss and whatever you choose. cress and heatran make an extremely solid combo as demonstrated by wolfey, the world champion runner-up. you can read the article about his skill swap team here:
http://nuggetbridge.com/reports/eggscelent-execution/