why the hell wont my trans stay cold

[SCIV]

Is your B&M before or after the radiator? My guess is before, and it is gaining heat from the radiator. Also, you verified the gauge/sending unit operation?

FWIW, I run only the largest Tru Cool up front (meaning ahead of the radiator), and my temps have never got above 150*, even at the track.

[farmtruc]

This time of year, an 80e and 2800 converter, i'd say it shouldn't be overheating, so it's not normal.
The single BM is more than enough to cool the trans.
I'd bypass the radiator and see how it acts, it's possible there is a restriction in the radiator. ( we have an SS here that has a restriction in the radiator, bypassed it and now it's fine).
Touch the trans lines just before the radiator, are they hot? This is to ensure fluid is flowing thru them.
200deg isn't hot, but it's on the warm side for this weather and the cooler you have, we see about 150-180deg in the summer on the highway.

If all this doesn't fix it, just drive it till it breaks, it might just be the transmission.

[Mhotrodscooter]

Ive been having somewhat of the same problem with my 06 2500 HD, how ever mine goes up to 250*. I've checked it with a heat gun & its only showing 186 max but gauge will be around the 250 range.
Most people said it was the interal harness.. Swapped it out with a OEM from GM & it doing the same thing. Check volts & ohms to & from everything & its still showing trams temp sensor is bad..
Haven't got around to replacing it again.

[02chevyls1]

the trans is brand new not even 100 miles on it and i would say average temp is 210 and thats bi passed the radiator even with the 60 and 3200 it went up to 180-200 no problem

[Mhotrodscooter]

Take a peek..
http://www.performancetrucks.net/for...-275deg-488953