RepairPal Certified shops can diagnose and repair your 1994 Hyundai Elantra. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
You have a seal leaking that is making it so pressure doesn't get to the proper level. Thus, your transmission cannot engage overdrive. Recommendations: Just drive it without overdrive activated and use another car for long highway trips.