First off, let me preface this by saying if your Hyundai is still under warranty, it is best to stick with approved fluids. Hyundai isn't known for being benevolent or forgiving when it comes time for a warranty claim. This post isn't for those with warranties or the true believers in the manual. This is for people that don't have the money and/or ability to readily get SP III
That being said, I've been doing some research on suitable alternatives to the Hyundai SP III ATF (a highly friction modified ATF). Why you ask? Because for me, the only place to get it is at a dealer for an (comparatively) extravagant price and a lengthy drive. Another reason is it doesn't seem to hold up as well as it should. When I drained mine out at 53K miles on the vehicle and around 20K on the ATF, it was very dark. I've seen used oil analysis reports that show significant break down of it in normal driving conditions.
Anyway my searching took me to ATF +4 (another highly friction modified ATF). Aside from the many users who have tried and liked it with no failures (I know, I know, it doesn't prove that it won't ruin your tranny), I have also spoke with a tech from Certified Transmission (Called to ask about the 2-3 shift flare it is experiencing) and while I had him on the phone I asked about the compatibility of the two. He said ATF +4 is fine for use in this transmission.
Further research found that my car has the F4A42 transmission, a Mitsubishi tranny. It was used in Chrysler, Mitsu and Hyundai cars. Mitsu and Hyundai spec the SP III, while Chrysler specs ATF +4 in their Sebring.
I also found that Chrysler has formally replaced the SP III in the rest of their applications with ATF +4
So, knowing that Chrysler completely replaced SP III in all their applications and uses ATF +4 in the same tranny I have in my car, I feel safe in using it too. In fact, since replacing the ATF with Valvoline synthetic ATF +4, the tranny has shifted smoother and better than ever.