Do I need a slip yoke eliminator iff....

[CALIFORNIA JEEPER]

I was looking into a 3" lift for my 89 XJ and wondered if I really need a slip yoke eliminator with a 3" lift..

[satan]

Hey - welcome ...

With 3" of lift you shouldn't need an SYE for your ride... if you plan on doing a few droopy trails, replacing your existing yoke with a YJ's yoke (commonly referred to as an extended travel yoke) will assure that your upper u-joint can support the sharper angles (this will be a bit more important if you are running and automatic)

Something else you may need to look at with 3" is how much of the yoke is "engaged" in/on the t-case output (may require minor lengthening of your driveshaft)...

[CALIFORNIA JEEPER]

I do have an automatic, does that matter?

[satan]

Automatics do matter -- some...

The body length of the automatic is longer than a 5-sp... the net result is that the stock driveshaft is 1" shorter meaning that you'll be operating at a steeper shaft angle than a similar set-up on a 5-sp.

In my experience, the "gotta-getta SYE" line is somewhere around a 4" lift for a 5sp of your vintage and maybe a bit less (like 3.5") for the automatics...
(of course the "plus" side of that is that you can get a drive shaft from a 5-sp shortened (if required) for our application, while the 5-sp guys are shopping for new steel!)