98 Grand Cherokee Overdrive

Hi all, I'm new on here AGAIN!! after several months (years?) away from the forum, I'm back with a question. My 98 Grand Cherokee Limited with 5.2L V8 and full-time four wheel drive, won't go into overdrive. We use this Jeep to chase after vehicles we purchase. Drive it out and then flat tow it back with a tow bar. Time before last, when I used it, it was working perfectly, but the last time I went on a trip, it wouldn't shift into OD. Any thoughts? No codes showing. Thanks for your help, it's good to be back amongst you all. -Rancher0