Well I did a drain and fill trans flush with toyota T-IV fluid about 6k miles back. I didnt realize that I hadnt filled the fluid all the way. But anyway it drive like a champ. NO rough downshifting into 2nd and not rough shifting at all. Well a few days ago I was checking all my fluids and realized my trans fluid barely registered on the tip of the dipstick. Well being the car lover I am, I went and bought a couple quartz and got it right into spec. Well it drive like crap again. ROUGH 2nd gear and all. To prove my theory I will leave it for a 100 miles or so and then drain some out again in 250 ml increments until it smartens up again. I will report my findings. Im no expert on transmissions but it seems, at least in my car, having the right amount of fluid builds too much pressure or something and it shifts like crap.