my laredo at times will not upshift past 2nd it is a 1991 with a 4L inline 6 .automatic overdrive tranny..when it does shift it works great but has a habit of not..it does not slip oil level is good and oil is nice clean red yet..seems the problem can happen at any given time..not sure if this trany is controlled by a powertrain control module or not .the kick down has been properly set and the tranny only has about 20,000 miles on it.when it does shift it shift smooth and works great..seems to work best in cold dry weather..hopefully someone else has heard of this problem efore and knows a way to fix it..

 

NOT SURE ABOUT 1991 ,
But Earlier cherokees and comanches had secondary circuits in neutral safety switch that told what
range (position) the transmission shift lever is in. Using a Google search your may find instuctions on how control this externally ,for testing , also information on how to diassemble and clean rather replace a neutral safety switch .(Big Money Savings} Have a Great Day ,,Steve