Normally, if the torque convertor (TC) is slipping, the O/D Light will flash or at the very least your CEL will come on with a code of P1744... IIRC.
If you have no lights, then I would try the fluid change as recommended and go from there. If the problem persists, then it is for sure a over heating problem. If the problem gets better, then ride it a week and drian the fluid again. This will as much of the older fluid out and give you a better mix of new fluid. If then things continue well after this, then I suggest doing the drain and fill every second or third oil change.
If you have lights, as mentioned before, then you will have to take it to a shop so they can run the proper tests to find out the problem. It is most likely a sticking piston, in the vlave body, that controls cooler flow. This can be corrected by either a Trans Go CD4Ejr Shift Correction Kit or by simply replacing the valve body.
If you have to replace the valve body, I would suggest that you get one from
www.axiom.com For more info on them,
here is a recent post where you can read what I have to say about them.
