If you use the filter media and gravel from the 29G in the new tank you should have little problems and won't have to "re-cycle" (nitrogen cycle). Use as much water from the 29 as you can so the water parameters aren't as drastic of a change. A 55G is only 16" longer then the 29G, hight and depth are the same. Not much more then that to add, enjoy the extra room, the oscars sure will. Oh yeah, it gets addictive, soon you will start looking at 75G and 125G.

Good for you for getting a bigger tank for your Oscar!! Too many people keep them in too small of a tank!!
My advice is avoid the temptation to add more big fish just because you have a bigger tank. I see too many people do that...try to add a Jack Dempsey, a large pacu or two. Pretty soon the tank is again overcrowded and the water quality declines. I have my Oscar in a 75 gal. He is a few years old now, very healthy, no "hole in the head" disease. He shares the tank with an old (12?) silver dollar, 3 angelfish (yes, angels!), a pleco, and a Raphael Catfish I have had for more than two decades!
Enjoy! Do partial water changes occasionally while siphoning some of the "gunk" out of the gravel. Bigger tanks are actually easier than smaller tanks, because you have more water to buffer any mistakes in water chemistry or temperature.

Well it sounds like you have had success with your 29g so just keep doing the same with your 55g. The advice above is good.....use some water out of the old tank, to start the cycle faster in the new tank. Don't over crowd because you have a larger tank......and enjoy the hobby.

just remeber if you forget sometimes, do water qualty testing weekly. that will keep him healthy. do these in the first ew weeks a loty to make sure there are no changes.