I used the RedLineOil telephone help to get a recommendation of what synthetic oil to use. The guy on the phone seemed to know his product well. I told them my reason to go to synthetic was for better protection when towing my 4000 lb. trailer. They recommended RedLine MTL for my manual transmission. MTL is formulated for easier shifting while still being heavy enough for the synchronizers to work.
The effect of the MTL is much easier shifting. Still not as easy as my previous 1984 Trooper-II 4 speed, but a lot better than my 1995.5 5 speed was with the original Isuzu oil in it.