'87 Cherokee auto trans.,feels like it's trying to engage the overdrive but it won't. At steady gas pedal appication it gets it and loses it, like an up-and-down RPM. Any ideas? Thanks

-Make sure your fluid is at the right level
-Search "TV Cable Adjustment"/"Kickdown Cable" (TV=Throttle Valve)
-Have you changed tire size or gears
-Search- "seeking gears" or something like that
-Change fluid/filter if it needs it

Just a short list, but a place to start.
Let us know how it's going...

~Good Luck!