Ok, you can eliminate a clogged bolt.

What about the amps you are driving your stepper with? Have you adjusted the pot on the board? Maybe it's too low and the stepper is not able to generate enough torque. Turn that pot up just a tiny bit clockwise and see if you notice a difference. Don't turn it too high or your stepper will run too hot. It probably should never need to be above 30-40% of its range starting from all the way counter-clockwise. Of course, each machine is a bit different.

What I do is turn it all the way down. I heat up the extruder and pull the filament out. Then I set a manual extrude of about 200mm at a slow rate, say 2mm/s. As the stepper is turning you'll be able to hold it still and overcome it. Very slowly turn it up until you can't hold it still and it feels really strong. Doing that I found that at a 25% increase clockwise from zero that my motors were strong. Also, having printed a lot since then, I've felt my motors and they do not get hot so I know I'm probably in a good place.