Change the fluid, and put in a new Transmission filter. Thats basic preventative maintainance. The Redline tranny fluid is some of the best. Highly recommended. Should definately help it shift smoother.
I did what what macrocosm said about the shift regulator thing.. and it's not worth it. The car doesn't go any faster, it just shifts harder, and is annoying when your going slow. It also caused some weird noises in my drivetrain that didn't go away after I plugged it back up. I do NOT recommend this mod.
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