When we flush the toilet, it fills very slowly, almost drip by drip. When we turn the shut-off valve off and then back on, it fills normally most of the time. Every once in a while, though, it will almost fill and then go back to the drip drip for a moment before the toilet is full.

What does the toilet fill valve look like?

When we flush the toilet, it fills very slowly, almost drip by drip. When we turn the shut-off valve off and then back on, it fills normally most of the time. Every once in a while, tho, it will almost fill and then go back to the drip drip for a moment before the toilet is full.
Toilet fill valve may have debris in it

It's a floating cup ballcock... So if I change this it should fix it?

You can remove the cap on top of the Fluidmaster, you will find a diaphram that is likely catching debris. Sorry I can't show pics but Speedball1 has great ones if he were here.

I always just replace them cause they are cheap anyway

If it is a fluidmaster then you need a 'fluidmaster seal' about 2 to 3 bucks. Make sure to get instructions, it is incredibly simple once you know how. There are many copy cat fill valves and I am not familiar with them. You may want to replace a copy cat with a fluidmaster 400. If this is on a kohler, it has a small restrictor piece in where you connect the supply tube. It can be pulled out. It is soft rubber.

Simple repair! You don't have to replace the ballcock. You have a FluidMaster ballcock,(see image) with a bad seal,(see image). Go to a hardware store and ask nfor a FluidMaster replacement seal #242. Shut the water off to the tank and twist the top off counterclockwise. The seal's on top pry it out and toss it. Replace with the new seal, button it back up and the ballcock's as good as new. Cheers Tom

The seal is in the picture at bottom left. The arm must be held up while twisting