I've noticed that when in O/D my transmission jerks when shifting from what I believe is 3rd to 4th at a speed of about 50mph. There is about 80,000 miles on the truck and fluid was changed at 40,000. I don't seem to notice any jerking when it is out of O/D. I'm going to change the fluid next week. Anyone have any suggestions or ideas? Does this problem sound like an adjustment? I have also noticed this problem when the engine starts to lug down and the transmission down shifts. Thanks for any advice. Ken