Hm. Well, regardless of whether you're at home or Walmart, I would trace the lines. The top one looks like A/C to me, and the bottom one looks like it might be transmission fluid.
Might be worth doing some Google searches, or even picking up a Haynes manual.
Maybe because it's cold here the opposite is happening and the the return will be warmer as it passes through the radiator?
Could be. Does the transmission have a thermostat? My truck has one, and won't send ATF to the cooler if it's below a certain temperature--part of the fluid change involves bypassing the t-stat (locking it open).
Have you hit up any specific forums? Sometimes guys will post DIY's on how they did whatever work, complete with pictures.
Once you figure it out, put markings on the lines so you don't need to figure it out next time.
I agree, your future self will thank you.
Draw a sketch of the Radiator and Transmission with any hoses.
Then add 'arrows' -> showing direction of fluid flow.
Knowing the direction of flow would also help if you ever install an Inline Filter.
from what Information I gathered usually the top line is the return line.
and now that I type this I remember when flushing the trans fluid out of my thunderbird that is the line i unhooked to drain out the old fluid while running it, I hooked up a hose around the fitting on the radiator to flush out the fluid.