Firstly, while this does not appear to be oxygen depletion, the first post impressed in itself that the bubbles could have helped rectify the problem. It does not. It's the surface movements the bubbles create that helps with the gas exchange thus preventing the oxygen depletion, not necessarily the bubbles themselves.
What test kit are you using? I am asking this to confirm whether the test results are actually accurate or not. There are a few times test kits can mislead you into thinking everything is fine when something could be actually wrong.
Brianp is not suggesting your fish has ich. Indeed, gasping itself is not often one of the common signs associated with ich. There are plenty others that cause this issue particularly gill flukes, silt irritation, ammonia intoxication, bacterial infections, flagellates, gill injuries, improper acclimation procedures and high temperature intolerance.
If your temperature is that way, what thermometer and heaters are you using? Perhaps the water is warmer than you think. I'd check the reliability of your equipments to ensure we can rule out temperature as the possible cause. It in itself may cause the intolerance of the fish to its environment rater than oxygen depletion. What was the temperature of the new water prior to doing a water change?
What are these fish you have in your 55g? When was the last time you added a fish in your tank? Did you quarantine your new fish? If so, how long did you quarantine them? Failing to quarantine your new fish makes your new fish potential threats to the health and safety of your old stocks. I would advise quarantining every new fish for at least 3-4 weeks. If possible, treat every new fish with praziquantel for possible gill flukes which are often common occurrences among aquarium fish.