U-Joint different front and back?

so I'm pretty sure I need to replace the front u-joint in my 04 crew cab 4x4. Are the u-joints the same for the front and back of the drive shaft? I'm having trouble telling them apart on the advanced auto website. Also, I'm pretty sure its just the front one that is bad but should I go ahead and replace both of them? If anyone has a part number to tell them apart it would be appreciated.

My problem is a driveline vibration at highway speed when I let off the gas.

 

OP, here is a link that you may find helpful, if nothing else you can always give them a call and pick their brain. Hit the "enter make and model to find a u-joint" link and scroll down to the bottom of the page for your information. FWIW, I always change these in pairs. But that's me, you may have a different approach.

If I'm reading it correctly, front and rear u-joints are the same. I hope this helps you out.

http://theujointstore.com/