what are the signs of a bad fuel filter.

First look at the manual and see if it overdue for a change. There can be fuel starvation after running a bit, or fuel starvation from the get go. A clogged filter can also cause premature fuel pump failure.

A clogged one won’t be able to pass the needed fuel flow rate to sustain high speed driving. That’s where you’d notice the symptoms first probably. You might notice hesitation, stumble, or a check engine light at higher speeds, indicating lean operation.

Another failure mode would be if it allowed gunk to pass through and clog the fuel injectors. Then you might notice the engine was performing poorly at almost any speed, including idle.