I am having sort of the same problem but a little diffrent. I have an 03 6th gen. If i take it easy and kepe my foot out of the gas the tranny shifts fine. I can drive a few hours on the high way, no problems. However if i get on the gas some, or a bit of stop and go traffic, it will start to shift hard into all the gears. Nothing ot hard but you notice it. I can trun then car off for 5-10 min and it will once again sift fine. The car has 78k miles on it. has had only the pan dropped and fluid replaced a few times over it's life. I have thought about do a total fluid exchange. Any thoughts?

 

Hi everyone, im new to this forum, and im in need of serious help. I have an 03 Monte, 3.8ltr automatic. My problem is: the transmission seems just fine at first, and shifts through all gears including OD until the car is warmed up (approx 15 mins) then it shifts Hard through all gears. o2 sensors replaced, tranny flush and fill with filter change but it didnt seem to help any. I am not wealthy by any means so any information will be helpful!
I am told by a certified mechanic that TransX is good in cleaning contaminants in the transmission?