Mine is doing the same. Reportedly the mapping does not account for temps above 40. It stops leaning the mixture and the sled runs fat losing power/rpm.
Somebody has a fix for it, I think you can have the ecu flashed (aftermarket) to cure this. I tried switching to the 91 non map and that brought some of the power back because it is leaner across the board. My belt has 3-400 miles on it, probably could use a fresh one and I am going to try lighter weights too.
I thought maybe it was the exhaust valves so I removed and cleaned them up last week. Helped some, response was better but rpm still only at 8000 max.
