A read end issue would be more constant after the first noise occurrence. Same with a transmission problem.

My guess is fuel related. Two gallons is not that much fuel when you hit an incline or a bumpy road. Fuel does slosh around and you could have sucked a quantity of air in the fuel intake.

I have had a similar issue with my YJ. Ran fine until the engine was hot and under load. Erratic fuel pump operation that could not provide full load required but held normal driving fuel needs. Hence, with low fuel tank level, the problem was more evident.

Keep your tank more that quarter full and drive the same section of road a few times. But, be prepared to replace the fuel pump...