A friend of mine changed his transmission fluid himself on his accord but used dexron III and now his transmission slips in 1st and 3rd gear. I always stick with genuine honda atf. I don't now anything about transmissions, but I do believe the certain kinds of ATF/other than honda atf can effect shifting capabilities. If you could feel the tranny slip I'd start to worry. Gotta love those honda trannies. This was happening before you changed the fluid so I'm thinking it's a transmission problem.
A total flush and fill might do the trick if it's a fluid problem and you should be able to feel/sense that your tranny is going bad.