I'm the owner of a 1998 Navigator-147000 miles- (and a 05 Expi) and this thing has such a hard 2-3 shift it snaps your neck and slams the driveline. The 1-2 shift is perfect , there is no slipping in any gear and the fluid looks great. I would like to fix it myself if I could and I would appreciate any info -thank you.
Sounds like 3rd is just right..I would be trying to fix the 1-2 shift....lol.
Sorry.... Auto trannys are really not my thing but believe you may have issues with your 3rd gear sprag. This is basically the series of clutches that engages the gear progressively before the band locks it in. Similar in function to a syncro in a manual tranny.
If your shift into 3rd seems to wait till much higher rpms before it shifts I would say with out a doubt your 3rd gear sprag is shot. I broke my 2nd gear sprag and it would do the same thing you described but the shift was also seriously delayed. Basically the sprag did nothing till eventually the band would lock it in anyways.
I suppose it could be issues with the valve body or sensors but really dont know?!