No experience with auto's/pot size but vid's exist claiming stress causes early flowering with autos. Same vid's claim roots hitting side/bottom of pots produces stress, early flowers, small plants, small yields. 5G pots/same cultivar might produce larger plants, even with 5G pots/new cultivar may see the diff .... did you try 5G?
i have tried 5 gallon pots , liquid nutes and organic nutes . my yeild with 5 galloon pots and liquid nutes were 4+ oz a plant when i swithced to organic my yield went down to 2 to 3 oz a plant was ok until i switched to the organic nutes