get rid of all but the GM's Psychic hood, the only point to have more then one is if your worried he'll die or something. Psychic hood in our codex allows you to challenge every psychic power an oppenent uses, no Line of sight, no distance check, you can even use it while in melee or a vehicle. You can only challenge it once, and you can't use aegis as well for the same ability, however the hood is still useful because it allows you to challenge psychic powers that arent affecting your grey knights directly where as the aegis does not, and the aegis wont help your vehicles, so at 2500 pts include one for sure.
i would reccomend you also drop a lot of the upgrades like concrete hero said, but take that into your GM too. Sure he's cool, but he has gobs and gobs of stuff you wont use in 9 out of 10 games unless you suspect a large daemon showing. In particular dont give him a daemonhammer, its pricey you just got rid of your GM level force weapon, which still kills any model out right because it takes away their wounds it doesnt cause instant death rule, so eternal hero characters dont have a defence to it.
the GM is awsome at assault, and wasted on ranged. You also cant give him destory daemon and holocaust, the codex says he can have one psychic power only.
i would strip him down, give him a psychic hood, maybe master craft his weapon if u want(can be helpful to make sure those hits land on other characters so you force weapon them down), hammer head is my favorite psychic because the army has good horde control with its default Storm bolters and it works in termie armor. Icon of the just is ok if you need to fill some points and u dont have more models to field, but i dont usually face any situations where a one better invulnerable save on him would have won the day.
i would listen to concrete hero too and take 3 land raiders, godhammer (normal) pattern, not crusaders. Crusaders are decent in theory, but again you already have mad bolter fire, what you dont have is good ranged armor busting. Alternativly you can take dreadnoughts if you feel confident you can get those Termies into melee without the assault vehicles, and i would probably take dreads with Lasscannons and missile launchers. Again you despritly need a ranged precense out of those heavy support choices, not taking one or filling it with horde control junk is gonna hurt you in nearly every game. (pro tip: use those 14 armor LR's as bunkers for your troops, dont disembark until you need to if there is ANY chance your troops will come under fire. You dont have many of them..and the shrouding is some where between garbage and poop, tank shock + incinerator = awsome as well)