Ford ranger runs at 4000 rpm highway speed.
Dunno what “highway speed” is but my Corolla turns over at about 2400rpm at 55mph. Assuming your Ranger has an automatic transmission, is the overdrive disengaged? That would keep it from shifting into the top gear. In any event, how long has it been since you checked the transmission fluid or had it changed?
Highway speed: 50-65, rpm 4100-4200. Started Friday night soon as I hit the highwsy. Transmission is a sealed unit, had fluids replaced at recommend ed time (150,000 miles). 160,000 miles now. Friday morning, spilled coffee on seat above drive train. Saturday, went on highwzy , everything fine (60 mph, rpm 2500).