I upgraded my trans cooler to the 2500 HD cooler, but I am running an aftermarket converter and didnt want any issues with heat. Temps rarely go over 170* which is good. Problems have come up with the cooler I run in colder climates. Originally Dodge made the 2500'd in 03 & 04 with a 26 row trans cooler (almost the same size as the radiator in height and width, depth is still the 1/2in or so). This was a great cooler and realy kept the temps down, unfortunately in colder climates where the temps plumits to the freezing/below 0 mark they ran to cold and caused the transmission to throw a code. So in 05' they switched to a smaller, yet thicker billet aluminum cooler. These cool down quite a bit but not as much as the 26 row one. Finding one of the 26 row coolers can be tricky though as the dealer does not carry the part number (at least the 3 I called in the area didnt) and order the billet aluminum instead. They are also rarelyin stock too.
For the gauge you can tap into a line, couldnt tell you which one though. I went with an Aeroforce Interceptor gauge, plugs right into the OBDII port and read the trans temp, engine coolant, and a slew of others. Simple to setup, simple to use and no tapping anything.
