1988 honda accord high rpms

my car is a 88 honda accord and the problem is that my car uses high rpms to maintain speed. it’s automatic so you figure once you get to 65 that should be 5th gear and theres no need for shifting gears well my car will seem like it’ll shift down to maintain speed then shift up then down but it wont hold a gear. causing to keep using high rpms. it has reached almost 6000 rpms at 50 miles per hour what can be the problem?

Get the transmission looked at by a professional ASAP!! There may be a mis-adjusted control cable or a bad speed sensor, but if you keep driving it like this, it may damage the transmission, and turn a quick and easy (cheap) fix into an expensive rebuild.

At 65 mph my 89 Honda Accord (5 speed) turns about 2250 rpm, less than HALF what you said yours does. Stop driving it and get the transmission checked ASAP. Rocketman