Does the inside fan shut off if you are still above setpoint ? or does it keep running but no cool air is coming out?
Digital thermostats can malfunction in unusual ways causing the problems you are seeing. To test, you can remove the thermostat and connect the R Y and G wires all together. This will bring on fan and cooling, effectively bypassing the thermostat. the inside fan will run along with the outside unit 100 % of the time . it will not shut off. If you notice it starting not blowing cold air after a while , you have eliminated the thermostat as a possible cause.
Alternatively you can go and buy a new thermostat and install it . set it at 65 and see if it keeps cooling without stopping.
If it is not the thermostat , that leaves a strong possibly of a problem at the condenser outside , like a failing fan motor, capacitor(s), or dirty condenser coil to name a few.