05 TJ Unlimited Rear Driveshaft Not Fitting

You will also need adjustable rear upper control arms if you don't already have them.
 
you need adjustable control arms to run a SYE. I am not sure if a SYE is needed on a LJ with 2.5” lift. What made you need a new drive shaft?
 
Watch this video, it will explain the SYE, drive shaft, and pinion adjustment. Wherever you order the SYE make sure to get a standard SYE and not a super short as Jerry mentioned above nor a hack and tap. Also, make sure it is in stock. I know for a fact that right now there are a lot of people listing things as "In stock" on their websites even though they don't actually have any in stock.

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