So basically I just finished battling the 7th gym and am wondering how solid/good my team is to progress in the game. Feel free to mention any changes that will improve my team.
Garchomp | Item: Dragon Fang | Nature: Timid | Ability: Sand Veil | Moves: Dragon Rush(Earthquake),Dig,Dragon Claw, Swords Dance
Blaziken | Item: Leftovers | Nature: Calm | Ability: Speed Boost | Moves: Blaze Kick,Flame Charge,Sky Uppercut, Swords Dance
D Venusaur | Item: D venusaurite | Nature: Serious | Ability: Psycho Call (Hubris) | Moves: Psychic,Leech Seed,Calm Mind,Moonblast
D Gardevoir | Item: NeverMeltIce | Nature: Rash | Ability: LightningRod | Moves: Calm Mind,Blizzard(Livewire),Thunderbolt,Icebeam
Tyranitar| Item:Tyranitar Armor | Nature: Calm | Ability: Sand Stream | Moves: Crunch,Rock Slide,Payback,Stone Edge
Thanks a lot 
Why is your garchomp timid.
And why does your Blaziken have flame charge when it already has speed boost
You should probably try to get a different nature on your Garchomp. The minus attack isn’t doing you any favors. For it’s moveset, 2 dragon type moves is redundant unless one of them is draco jet for priority. It would be best to replace one (iron head is a good coverage move) Replace Dig with EQ.
Same goes for Blaziken. That negative attack nature is hindering it and the two fire moves are redundant. Drop flame charge for anything really, it depends on how you want to play. Crush claw, night slash and rock slide are all solid options. Poison jab would give you a fairy out. Baton pass is also very powerful. Blaze kick should be fire blitz. Sky uppercut should be High jump kick. I’m personally running an adamant speed boost blaziken with Fire blitz, Hi jump kick, baton pass and hone claws because I have a noctem spiritomb.
D Venusaur and D Gardevoir are pretty standard. I would absolutely run livewire over blizzard. If you have something that can boost accuracy than blizzard over ice beam.
T-tar has a hindering nature and a redundant moveset as well. It also depends on how you want to play it. Pick between either rock slide or stone edge. If you are playing an offensive set t-tar has some decent setup options. If you chose D-dance go with crunch, Curse go with payback. Stealth rocks is a good option, you can run him as a pursuit trapper. There are loads of options as it has an incredibly deep movepool.
As for a six member, you don’t have a fairy killer as is and half of your team is weak to ground. Gengar could be a solid option. It gives you a fairy out and 3 immunities with a good supporting movepool.