I took it to the shop and just heard back from them. Clogged catalytic converter. Getting a new one shipped in and welded on.

 

Catalytic converters don't become restricted just for no reason. There is a reason and if the shop replacing it does not find and correct the reason,it can repeat the performance.

 

I have planned on installing an oil catch can and have upgraded to 5w30 oil.

 

Hi do you have updates?
did new cat fix the problem?

I have same problem with my 2018 Tucson
Car seems to run fine on flat road, but as soon as it hits any kind of uphill it just drops down to 20~30mph and refuses to go any faster.
If I hit the gas hard, RPM shots up but still no power.
I tried manually shifting down to lower gear, it doesn't help.