You say you were in an -8 then thrust reduction would most likely occured at 1000' agl. I've operated the -8 out of JFK, both short and long haul and at MTOW, under most ambient conditions, this would be normal. Sometimes, more frequent than many would think, when relatively light weight (think short haul) the minimum climb thrust is higher than the take-off thrust especially when using TO2 with max ATM. This actually causes a thrust increase when going to climb thrust.
As mentioned above most likely reason is tyre imbalance which can occur for a multitude of reasons and gets written up by the Tech crew for checking at the next stop.