If you bought an aftermarket fan from an autoparts store it is probably too small. I think about 2500 cfm is the minimum for a worked 235 or 261. Mine is a 16" 2500 cfm and it draws about 15 amps when running. I had to look for it to find it, most of the fans were for auxiliary use and were less than 2000 cfm. My truck never overheats but it never gets very hot here and I haven't hauled any heavy loads in stop and go traffic. I've sat in the dump line for an hour with it running and no problem, though.
In the meantime, you may want to check your antifreeze mixture. 50/50 doesn't transfer heat as well as 30/70, and you can add some water wetter for a bit of added efficiency. Just make sure you check it before winter.
