Conor Tadler Asked: How Can I Improve My Party For The Elite Four In Pokemon Diamond and Pearl?

I have been training my party for the elite four, and this is my current one:

Garchomp lv. 52
-Rock Climb
-Flamethrower
-Dig
-Dragon Claw

Palkia lv. 52
-Surf
-Ancient Power
-Dragon Claw
-Spacial Rend

Lucario lv. 51
-Rock Smash
-Dragon pulse
-Aura Sphere
-Earthquake

Gengar lv. 53
-Dark Pulse
-Strength
-Psychic
-Shadow Ball

Luxray lv. 53
-Shock Wave
-Spark
-Crunch
-Thunder Fang

Crobat lv. 53
-Air Slash
-Defog
-Fly
-Poison Fang

I was looking for criticism in terms of how high I should level these pokemon, any changes/shifts I should make to my party (i have mid level 40 area torterra, roserade, rapidash, gyarados), and any techniques in order to combat the elite 4 in Sinnoh. Thanks in advance!