These challenges (snark, slacking, rudeness, not wanting to do boring work) are all, IMO, exacerbated by being gifted. It was our experience that having the hardworking kids around our bright procrastinator was extremely helpful for teaching her how to organize and prioritize. The bright, hardworking kids were excellent role models and did not give positive social feedback for snarky slacking.
Back to your actual questions!
The links from Indigo are good ones and the questions on the sites are spot on. If at all possible, I'd go and observe the class your DS would be in. Look at the textbooks (snap a quick photo of the cover of the math, reading, & language arts books so you can research them online), talk to the teacher, see if there are any parent groups that you can talk to. If it seems fine to you, I'd then arrange a visit or shadow day for your DS. If he buys into it and wants to go that can really enhance his experience as a student.
If he goes to the gifted program and it does not work out, what are the options?
From your previous posts it does not sound as though your DS's current situation is working well for him…the gifted program may or may not "solve" everything, but if you think it is a good fit right now it will probably improve things for a while. Our experience has been that every year new solutions are needed and new focus in one area can compensate for boredom in another.
The other aspect to this is friends and peers. Does your DS have at least one good friend now? Is he invited to birthday parties, play dates, or outings? If not, that would make me consider moving him more strongly. In 3rd grade most kids still have very fluid friendships (IMO) and can make new friends in a new class --perhaps on their own, perhaps with scaffolding from parents.
