I had a 98 & I had the Helm repair manual. There were pretty detailed procedures for all the codes. I fortunately never had to deal with a tranny problem, and I don't own that car or book any more.

The list that I kept simply says
P1768 (16) stuck in 4th; L-U-Clutch not engaging
I didn't 'save' the actual diagnostic procedures...

The lockup solenoids are at the front of the tranny, sorta against the radiator, #8 in the picture. Without better information, you could just look for loose/dirty/corroded plugs. Even if you need those valves, that's WAY better than needing a new tranny.