Looking at Buying 94f150 with tranny problem

Im looking at buying at 94 f150 with a transmission problem. Not sure if this is a good idea when it might need a new tranny. When you drive it in 1st and 2nd it is fine, when you drive it in 3rd is slips and bucks but this problem is only intermittent. It has a 302 and 4x4 with 126k original miles, one owner.

Any suggestions?