transmission cooler

For a plate&fin transmission cooler, what would the best direction to have the inlet and outlet fittings point? up,down or to the side. Which way works better? I'm installing a larger trans cooler for towing in colorado rocky mountains

 

Whenever I have installed trans coolers, I have always installed them horizontal or with the fittings on the side .
Seems the cooler fits or adapts easier with the cooling lines placed on the side but with this said ,I beleive you can install them up/down or side to side as the transmission pump will still pump oil through it both ways .

 

There is a way that some manufactures say to mount them, I cant find the link now but I would suggest checking with the manufacture.

 

If you mount it horizontally, make sure the inlet is connected to the bottom port, and the return line is connected to the top port. Otherwise you'll never get the air out of it.