I have a 2016 Kia Sorento (3.3L V6 petrol) with 6-speed auto. Earlier in the year the transmission would regularly downshift with harsh 'thumps', making it unpleasant to drive. After a number of tests, Kia replaced the valve body and it fixed the problem. The car then drove without issue for a number of months, but now has started to exhibit the thump downshifts again. Upshifting 1st-2nd can also be harsh at times. The fault is nowhere near as bad as the original problem and drives fine most of the time, but I continue to experience the occasional harsh gearshifts. Interestingly, it usually only occurs when cold. Considering the valve body has already been replaced, could it be related to transmission fluid, or something blocking a port in the valve body?
It wouldn’t hurt to change the fluid, but it’s more likely to be in the valve body.