Any IH from the 06s to the 86s were kinda miserable SOBs to get in gear IF the clutch or shifter linkage was just a little out of ajustment.  Maybe all you needed was some ajusting. If the Clutch was out it wouldn't want to move too well down the road, Slipping.    I think you might of got a little hasty replacing the clutch. 

 I ran a few of those miserable tractors in my youth. 2 of the neighbors had 706s on loaders & That was what I had to use to feed the tub grinder costom grinding I ran for 1 of those neighbors.    

 Like most say YOU BOUGHT A OLD TRACTOR, it ain't no virgin.