Well, if it's in-game, then this is what I'd do:
Swap Infernape's Mach Punch for Punishment. With 108 base speed, being outsped is hardly a concern. The only Pokemon with base speed above 108 which might die in one Mach Punch are Persian, Weavile, Absol, Sneasel, Ambipom, Raichu and Heliolisk. Anything else would hit you anyway, so the 3x stronger Close Combat is much better. Punishment could hit Psychic types hard, especially if they buff themselves.
For Gyarados, get rid of Rock Smash for Thrash or Bite. Whenever you get Waterfall, get an HM slave or swap it with Aqua Tail if you want accuracy over power. Or finish the puzzle at the circus and swap Aqua Tail for Dive..
Gardevoir seems fine. If you need a Grass move, which you seem to have none of, you can teach it Magical Leaf. If you need it.
Exploud could use some breeding to get Flamethrower and Ice Beam. Same for Nidoking. This could help you: http://www.pokemonreborn.com/forum/index.php?showtopic=8566
Oh, and swap Magnezone's Magnet Rise for Screech, keep Metal Sound, helps the team.
There's also the guy in 7th Street that changes natures. I'd recommend Adamant for Infernape, Adamant or Jolly for Gyarados, Modest or Timid for Gardevoir, Exploud and Magnezone, and Hasty or Naive for Nidoking.