You don't need to have your oil changed at the dealership you can have it changed anywhere just make sure you keep your receipts and use the recommended type of oil to maintain the warranty.
Telly requires SAE 5w30 synthetic at least. If you want to keep the GDI engine running great then look for ACEA A5/B5 certification. Pennzoil Ultra Platinum is best on the market and recommended by many High End brands like Ferrari, Dodge Hellcat & Demon, SRT, BMW and others. Pennzoil platinum alter would be another good choice but I can't find whether it has the certification or not but would work in a pinch.
Kia uses Castrol Edge Titanium full synthetic which also has that ACEA certification.
OK, found the Manual..it calls for 5w30 (yes, conventional comes in 5w) They recommend ACEA A5 for better fuel economy (found many semi synthetics that meet this spec. But it says you can use ACEA A3 if 5 is not available or GF-3 which many conventional oils meet. So it does not specify full synthetic oil.
I'm not telling you to change anything, you keep on doing what you are doing. Just correcting mis information about the Telluride REQUIRING full synthetic oil to keep the warranty intact when it actually does not. That is all. Congrats on your 3 cars and hopefully, you will make it 4.
With as cheap as synthetics are today, why is there even an argument about it any longer? For a few dollars more , you get superior life and protection.... I haven't used conventional oil in 10 + years.
Most all of my vehicles go 10K on a change, and analysis proves the oil still has life left even then....