transmission prevention maintenance

My 99 ram had the 5.2 motor and automatic transmission.
I plan on doing a fluid and filter change this weekend, and thought maybe I should add a cooler also, if so, what one?. Would that help prolong my trans? Also anything else I should do to make sure it continues operate perfectly?

Transmission preventive maintenance

A cooler will help, but make sure you don't already have one. A lot of Rams came with an extra cooler from the factory, maybe with the towing package? If you don't already have one, adding one will help. One thing I do with all of my transmission services is add a bottle of Lubegard Platinum additive. Real tranmission guys, that actually rebuild transmissions and have to stand behind them, use this stuff on the install fill, it seems to be one of the only trans additives that really works and prolongs the life of the trans while keeping it cooler. Lubegard say that by using the Platinum you can use Dexron in place of ATF +4, however I don't do that; I do some towing with mine, so the synthetic base of the +4 is good to have.

If the transmission lines go into the radiator that means no cooler right? And with that what size cooler should I get?

Yeah, on my Ram (01 5.9 gas with tow package) it's obvious that the line cuts out to the external cooler then back to the radiator. If yours only goes to the radiator, you can add an external cooler. It's said to add one as big as you can fit, well with the Ram you can pretty much fit anything in there. Flat plate coolers are supposed to be more efficient per size than tube and fin coolers, but the tube and fin are cheaper. I would get one big enough that I could make up some solid mounts for it, they come with plastic 'ties' that go through the radiator or AC condensor to hold the cooler; don't use those unless you have absolutely no other choice, they will break and let your cooler bounce around and damage your condenser or radiator, or they'll damage whatever they're hooked to themselves. It's more work to make up some mounting brackets and mount the cooler solidly, but it's worth it in the long run.