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

Fuel starvation!???

Was it hot out?
Are you running stock pump gas with alcohol?

My bone stock 67 273 would do that but only when it was really hot out. First time it did it I thought I floated a valve. Scared the crap out of me.

Lately I have been buying alcohol free gas and I have not had the same issue since, and I have tried to get it really hot, ideling in gear, stock temp guage at 1/2 way mark (Normally it sits at 1/4 to 1/3) And no more problem