904 transmission blows 2nd to 3rd shift under heavy power

It was hot, 88 degrees, but she runs cool 190 all day long. I run premium gas in it, which is supposed to be ethanol free. RPM were around 4000 so I don't think its floating the valves. The kickdown works fine, I have the Lokar kickdown kit. It's always kicked down when I need it to. Could be fuel starvation, but it only bucked for a half second. I hope its not the tranny.