1975 gmc jimmy not shifting?

[Randy]

my jimmy is a full time 4x4 ive taken the front shaft off for repairs, and noticed that the truck seems to take longer to shift gears and shifts a little rough. with all the work ive put into it, its just about fully restored new engine new tranny, and now this problem, was wondering could this be the transmission modulator?? and how hard is this to change out. thanks

 

[dodge man]

check the vacuum line to the modulator it may be collapsing and causing it to get low vacuum and that will cause it to shift at higher speeds,that's usually what cause it on those vehicles,that or the kick down linkage,good luck.EDIT if its the modulator that's bad there's just one line and one bolt to remove to get it out,but be careful and don't loose the little stem that's in the transmission it helps it to shift,when you pull the line off look for transmission fluid in the vacuum line that's an indication that the modulator is gone bad on it,good luck with it.