It's always good to do a few diagnostic steps before you start replacing parts - saves time and money. Pull the thermostat out a test it. Put it in some hot water on the stove along with a thermometer. Makes sure it is fully open at the correct temp. Then check the lower radiator hose. It should be very stiff - difficult to squeeze with your hand. If it's soft and pliable, then it's probably collapsing and interrupting the coolant flow. Remove the radiator cap and run the engine until warm. Look in the radiator opening and make sure you have good coolant flow. If not, replace the pump. Finally, look inside and outside the radiator. If you've got a lot of rust and scale on the inside, or leaks on the outside, replace it. Replacement parts are so cheap, I don't feel it's worth the effort to have one repaired or cleaned. Unless you're really on a tight budget and just want to buy a little time. As for the replacement, it depends on what's under the hood, and where you live/drive. If you have a stock I6 and you live in Minnisnowda, then a stock two row part will work just fine. On the other hand, a big block in Phoenix with A/C needs the biggest aluminum radiator you can find, and then some.