I usually use a Factory Service Manual (FSM) for my info and still have the one for my '94 (rear ended and totalled last year) and it specifies GL-4. When I checked the owners manual (yeah, being a packrat I still have that too) it does say GL-4 or GL-5.
When I had the 94 Tracker, the local trans shop was servicing my Dodge 3500 and while talking to the tech about the rough shifts in the Tracker, he mentioned the differences between the GL4 and GL5 and told me do not use the GL5 in the Tracker cause it doesn't have the pressure rating of the GL4 and causes the rough shifts due to shearing of the oil in the syncros("pressure rating" and "shearing" were new words to me) and to use Redline.
Redline fixed the problem so I assumed he was correct. I guess if the owners manual says its OK, then GL5 must be acceptable and the tech was incorrect.
Sorry for passing out bad info...