I've searched the archives and haven't been able to identify a similar problem. I have an 01M and when it shifts from 3rd to 4th, the car forcefully lowers rpms (slows the car down slightly), and then finally shifts. Overall the shifting takes about 3-5 seconds when doing the shift. It really feels like the brakes are being applied while the shift is taking place.
I changed the fluid about 10k miles ago, and no problems. I rechecked fluid levels and it seemed perfect. Fluid had a slight brown translucent color, but did not smell burnt.
Any help would be greatly appreciated. As stated above, I am not getting any codes either. Could this be a torque converter problem?