MD is a notoriously streaky scorer. Get used to it.
The one thing that Donny "I'm as fast as LeBron" Marshall said that was egregiously wrong last night (other than the claim that in his playing days, he was as fast as LeBron) was that MD is a better spot up shooter than shooter off the dribble.
From everything I've seen from MD since he's been in the NBA (the Mavs are my west team so I've seen him quite a bit), this is completely backwards. He will never sit there, wait for the ball, catch, and shoot in rhythm. Instead, he needs to have the ball in his hands, put it on the floor, dribble around the defense, and shoot on the run. Whether a floater, fadeaway, or pull up jumper - this is how he scores.
Sometimes I wonder if Donny actually watches the games, or if he's watching PGA replays.
In any case get used to Marquis throwing up bricks consistently. I still don't have any problem with it. When he's on, he's on. But when he's off, don't get frustrated.