Transmission slipping..

If it winds up (slips) between the 2 to 3 shift it could be the throttle pressure linkage isn't adjusted right. You need to lengthen the linkage to apply more pressure to make it shift firmer. I always start by adjusting the linkage so it's pushed all the way back at full throttle. Then test drive it and if it winds up too much before it shifts shorten it up a little at a time until you get it shifting where you like it.