I'm wondering if I have a transmission or clutch problem or both. Any help or input would be appreciated. Thanks.

The car is a 1992 Civic CX with 153,000 miles. When driving on the highway its sometimes pops out of 5th gear on its own, its not sudden, it just gets out of gear and I put it back in. When downshifting into 2nd it does this as well if I try to slow the car with a lower gear.