6000 stall is pretty loose, so it will build a lot of heat. But with 400ft runs it still shouldn't get that hot and it doesn't sound like you are on the converter too long to build that much heat. Check to make sure that the lines aren't getting heated by a header.
I know it all goes pretty quick, especially in a new combo, but try to see what the rpm's come down to after the shift at 7200. They should come down close to the 6000 and then start pulling up again.
Good luck,
Bill M