[svx_commuter]

Well this is a tough call becasue we have to go off of what you hear when the engine speed increases. I do not know how anyone could tell you if the tranny slipping or the tach screwing up.

I can suggest that you have the 4EAT performance checked. This means that the pressures in the transmission are checked at various conditions to verify that all is well.

You could also pull the line pressure resistor (by the battery) to see if anything changes. This increases the pressure to the clutches and takes the TPS out of the picture.

The transmission can slip becasue the clutch plates are worn. It you remove the pan and look in the pan it might tell you if the clutches are on the way out. You would see metal "flakes" in the pan.

The external filter could also be blocking the flow increasing the temperature in the tranny. It would be good to replace this if it hasn't been done and if the X has one.

I like the Lucas tranmission additive. If you try that I would suggest 2 bottles.