Get the vehicle going about 45 mph in high gear (not overdrive). Shut off the engine while still in drive and in a cadence, depress the accelerator to the floor three times. (1-2-3) After this,put selector in neutral and restart. Continue driving, if the shift improves, repeat same procedure. Let us know if this corrects the problem.
Conner

Over the hill but still climbing.
88 Montero 2.6L auto, manual hubs, cooling fan conversion gps,recurved distributor,LSD Diff.