The thing you're calling "transmission" is actually called "differential." Sometimes it's called "third member" assuming it's the kind where the carrier and gears drop out of the housing as an assembly.
The "4 78" means the gear ratio, which is the number of turns the driveshaft makes for every turn the axles/wheels make, is 4.78. I found a table there
which lists the 029CA104 part number with the following suffixes: 5X=4.33; 7X=4.56; 1X=4.78; 2X=5.57; 3X=6.50; 4X=7.17. This matches the data on your tag.
First question is this: is your speed limited by engine power, or by a governor limiting engine RPM? If the latter you could swap your gear set for the 5X or 7X part with 4.33 or 4.56 ratios and get more speed out of the same engine RPM. But if your speed is limited because the engine is already giving all it has to give, I think changing gears would give worse acceleration and no gain in top speed. Might even be worse..?