Slant 6 power issues

Bewy said
Could have two [ or more problems ].
Runs fine at idle but no longer creeps in gear? Maybe brakes are binding.
How long has it been since the carb was serviced/rebuilt?

Too long. Gaskets leak. My mom bought the car when I was 3 and a half or so and as far as I know, that carburetor has never been serviced