Flush or fluid add? on 2007 Kia Spectra

0ver 98,000 miles. Trans fluid is brown, needs to be changed. Dealer recommended a flush. Everybody has a different opinion. So flush or just add fresh transm. fluid? The vehicle slows down at acceleration and when gains steady speed, runs just fine.

Asked by for the 2007 Kia Spectra
Unless dealer will guarantee the trans will be fine after 'flushing' , I would recommend a simple drain and fill , with a filter change , if that applies to that vehicle. Would also recommend ONLY using KIA ATF.
Dealer does not guarantee anything. They said one never can know when transmission can go down. I know that the flush has been done on this 2007 vehicle around 70,000 miles. They recommend doing it again.
kia does not recommend flushing transmission becausing of introducing chemicals into the trans drain and rellil
1 more answer , 1 more comment
would flush first then change filter and gasket and refill
You think it will be fine considering the high mileage? The flush was done around 70,000 miles. By the previous owner.