How about Psychic for Psybeam and Thunder for Discharge.
Garchomp has been put in to the Uber tier recently.
Thunder has iffy accuracy, IMO Discharge or Thunderbolt will be better.
IMO it should have Ice Beam as electric + ice will hit everything for 100% par Magneton/ Magnezone and Lanturne.
If you use any attack like Hyper Beam or Giga Impact you should put it on to a Slaking as it will lose every second turn any way.
Once the team is finished do you want to test it out against my team?