Potty Training Relapse? Help!

Hi everyone! Hoping for some advice with everyone's favorite phase...potty training! Sorry for the long post, just want to get all the details out there about what's going on and what we've tried. Thanks so much in advance for any advice!!
DS is 2 years 9 months old...we've been potty training for about a month and a half and at first he did GREAT, at least with pee. He never really pooped on the potty but we were working on that...pee training was going great. Going on the potty every time we took him, going about 2 hours dry between potty trips, telling us when he had to go, minimal accidents, etc. We started with the sticker chart and M&Ms, but didn't need them for very long. He also started to game the system (asking to go pee every 20 mins just to get an M&M, forcing himself to go when he didn't need to and getting very upset if he couldn't because he wanted the M&M, etc). We didn't think this was too healthy and he didn't really need the incentives anymore, so we weaned him off of them and after a few days, he was going potty normally without any incentive (still just pee).
After about 2-3 weeks of the pattern above, we went ahead and put him in big-boy underpants. Figured it would help cement the idea of staying dry and maybe encourage him to poop in the potty too. He was very excited to get big-boy underpants. However...BIG mistake...no idea why, but he completely went backwards. Peeing every 30 mins, not telling us when he had to go or even when he was wet, completely back to square one. After 2 days of this, we put him back in pull-ups, which he was not happy about...he wanted his big-boy underpants and we explained that he could have them again when he stayed dry and peed in the potty like he did before. He asked about it for a day or two, but it was a non-issue after that.
Now that he's back in pull-ups, it's not as bad as the days he was in underpants, but he is definitely having several accidents a day (where he used to maybe have one, if any...he often even stayed dry through his nap), sometimes protests going potty (but not always) even when he clearly needs to go, will sit on the potty and not go, then go 10 minutes later in his pull-up, etc. He originally only took a few days to "get it" but this has been going on a couple of weeks.
He's SUPER verbal and definitely aware of what he "should" be doing. He tells us right away when he's wet, but not before he goes like he used to...and also, where before if he had an accident he told us and seemed neutral or somewhat "oops, I shouldn't have done that" about it, now he usually tells us in a sing-songy "this is funny" way. I'm worried going back to the chart/rewards system will get him too attached to the rewards again, but it did work the first time in terms of guiding his behavior...until it did so too much and we had to stop. We make sure he gets lots of positive reinforcement when he does go in the potty and has a dry pull-up, and when he has an accident we tell him that big boys go potty in the potty, not in their pull-up but try to make sure we don't act mad or upset. However, we're not making any progress from where we are right now, which is way behind where he was a couple of weeks ago.
Anyone gone through anything similar? Any ideas on what we should try? Do we just wait it out? Back to underpants and persevere through the accidents till it sticks? Back to rewards? Rewards specifically for staying dry instead of for going in the potty, maybe? Please help!