My Yukon's transmission is slipping and I need someone who knows what they're doing

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So I've got a 2016 GMC Yukon that I use for family trips and honestly it's been such a solid vehicle, but about two weeks ago I started noticing this really unsettling hesitation when I'm accelerating from a stop, like the transmission is taking too long to engage and then suddenly it clunks into gear, which is definitely not how it used to behave. I took it to a local garage and they said it might be the transmission fluid needing a change, so I paid for a flush and filter replacement, but honestly the problem is still there and if anything it feels like it's getting worse. I'm starting to think it could be something more serious like the torque converter or maybe even internal damage to the transmission itself, and I'm honestly dreading what that might cost to fix. The thing is, I really don't want to take it back to that same garage because they clearly didn't fix the issue, and I'm worried about taking it to just any other place that might not have the right expertise with these GMC transmissions. I've been searching around and it seems like finding a proper Dubai GMC accredited repair shop is really the way to go because they actually have the right diagnostic tools and technical knowledge to properly figure out what's going on with these specific vehicles, rather than just guessing and hoping for the best. Has anyone else experienced transmission issues with their Yukon or Sierra and actually found a shop that properly diagnosed and fixed the problem without charging a fortune? I really need to get this sorted before it leaves me stranded somewhere with my family in the car, and I'm hoping someone here can point me in the right direction.