[Batmanntexas]

The more I think about it, I do believe it is because of the increased cubes. While I might make the same peak HP as you, in just day to day driving conditions, you have 40ci+ more engine displacement generating heat that the stock system is trying to contend with.

I think once you switch to the upgraded radiator, your problems should dissipate greatly, if not entirely. The only variable left would be the airflow rating of the stock fans, but I would think they would be sufficient for street/strip duty. Road course action might call for a different solution.