Round or Square Cooler... how can you tell?
If you have a 2003, you should have a round style cooler.

If you have a 2005 or newer, you have a square style cooler.

If you have a 2004 model, this is where it gets tricky. Most 2004's have the square cooler, but a small percentage were produced with the 2003 round version. The easiest way to tell? Check your VIN code. A sample VIN code is: 1FTRW21P24EB10150. In the middle of the VIN code, you see the digits "4EB". The 4 means that it was a 2004 model year. The "E" denotes which production plant built your truck. In this case, E is for Kentucky. Lastly, the "B" is the start of the sequence number (the last 6 digits of the VIN). Some early 2004 models have a "4EA" code. The "A" denotes the early build and most likely is a round-style cooler. The "B", "C", "D" or more all denote later model 2004 builds with square style EGR coolers.

 

Which do I have a Round or Square EGR Cooler?
Symptoms of a Bad EGR Cooler