My Ford Explorer started slipping between 2nd and 3rd gear - rebuild or replace?

Been driving my 2016 Explorer for about three years now with no major issues, but last week on the way to school dropoff I noticed the revs flaring up when it shifts from second to third, almost like it's hesitating before catching the next gear. No grinding noises or check engine light yet, but I know transmission problems don't get better on their own. I took it to one shop in Rashidiya and the guy immediately said "full rebuild, 6500 dirhams" without even test driving it, which didn't feel right. Another mechanic mentioned it could just be low fluid or a solenoid issue, but he doesn't do transmission work himself. I found a mobile service online offering High-Quality Gearbox Repair from 800Sayara Dubai and they claim they can diagnose on the spot with a scan tool and even drop the pan to check for metal shavings before giving a real answer. That sounds way better than trusting someone who just wants to pull the whole unit out. Has anyone here had a transmission issue that turned out to be something simple like a valve body or just old fluid? I'm hoping I'm not looking at a full rebuild, but I also don't want to waste money on bandaid fixes. Also curious if these mobile guys actually do the repair on location or if they just diagnose and then take the car away.