Right now it might not be your technique that is holding you back but time of day. I have not caught a cat in the last 3 weeks except for early in the morning up to about an hour after daylight or at dusk and after.
As far as fishing in rivers, look for holes and depressions. If you can find a hole that has a long flat on the upstream side of it the cats will wait just under the shelf to block themselves from the current and wait for food to be brought to them by the current like a conveyor belt. Some holes are better than others, if you can get away from the holes that get the most fishing pressure you will find more fish and bigger fish. This will take a little scouting on your part. Also, if you can find a hole with some snags, structure and trees that are hanging over the bank, you will find bigger and more fish; they love cover. They will also come out on the flats after dark to feed. Hope this helps you out.