Transmission lines... which one is the return?

[CSVT#49]

So I'm about to tackle the transmission flush and fill, but I'm not sure which line is the return line? Here is a diagram below of what my setup looks like. I know I can disconnect one line and then start the truck to see which one is which, but I'd rather get it right the first time. So if you know which line is which, please chime in. Thanks.

 

[CSVT#49]

Figured I'd respond to this seeing as I just finished the flush and fill, which for those wondering there is a 'How-To' in the how-to forum for it now.

The return line is the one leaving the radiator and coming back to the transmission, which I believe ends up being the top port on the transmission.