My last genI had a non-lockup, and though I didn't put many miles on it, it definitely could've used the lockup. With larger tires it sometimes lit the trans-overheat light... my current auto drops 3k when locked, and you can slowly increase throttle without getting the annoying down-shift/upshift repetition when climbing modest grades, etc. Definitely worth the swap if you don't have it already. Sorry I can't provide numbers, but mitsulvr may post up with what my former 89 had for a trans. It might be handy to know the month of manufacture too, to get a handle on when it changed over?