Lower gears and still slugish.

Check to see if the throttle pressure linkage is actually operating the lever on the transmission. When you are at WOT, the lever should be all the way rearwards. If this checks out, disconnect the linkage from the lever on the transmission & push the lever rearwards. Release the lever & it must spring back. If not the weld that attaches the segment to the shaft may have broken meaning that the Kick-down valve is not being operated at WOT. I've seen this a few times. It is not advisable to drive around with this condition. A disconnected or non operational TP linkage will toast a transmission very quickly.