9" doesn't have a carrier break, so there's no such thing as "thick" 9" gears.
But if you can get thick 4.56 gears for the D44 (I dunno what exactly is available), then there's no reason not to run them. Technically, they're heavier, so there's more power loss to rotating mass..... but you're not running the 1/4 with this truck.
They might also be more expensive... the cost of a new carrier would figure into that, too.