I don't think anyone posted this, but in the GBA port, the controls in Rocket Rush are reversed.
So, while left would make you go right and right would make you go left on SNES, left makes you go left and right makes you go right on GBA.
Oddly enough, although one would think it'd make that stage easier, I actually found it HARDER, as I was so used to the SNES version's controls.
Additionally, the first half has a crapton of Green Buzzes added for pretty much no reason (it, with the different controls, makes that part even HARDER!)
And the second half has several Fuel Barrels in the area, so now, even if you mess up, like, 6 times, you can still make it.
And, the Star Barrel seems to be missing in the GBA stage.
Finally, Rocket Rush doesn't have unique music. Instead, it uses "Jangle Bells" (GBA's replacement for Hot Pursuit), and Stampede Sprint (which previously used Hot Pursuit), now has a unique track.