>The user creates a bizarre area in which slower Pokémon get to move first for five turns.
-- Pokemon DB on Trick Room
>Gyro Ball inflicts varying damage: the slower the user compared to the opponent, the higher the damage, up to a maximum base power of 150.
--Pokemon DB on Gyro Ball
In Trick Room, the slower Pokemon moves first. Its actual speed is not increased. Since the damage of Gyro Ball is based on the speed of the user(25 × TargetSpeed ÷ UserSpeed), and that Trick Room doesn't increase the Pokemon's speed, the damage will be the same.