Just saw this in an Isuzu Service Bulletin service (Alldata) that I subscribed to. Net is that 1998 timing belts don't need to be replaced until 100K (not 75K like the original service manual states). One less project for me to do this weekend!

Here's a copy of the service bulletin:

1998 Trooper (UX) / Rodeo (UE) / Amigo
(UA) models

SERVICE INFORMATION:

In the past, the timing belt replacement for the above affected vehicles has been recommended at every 75,000 mile intervals, regardless of driving condition. It is now recommended that the timing belt replacement interval of the above 1998 Isuzu models follow the same timing belt replacement interval as its 1999 model year successor. The new recommended timing belt replacement interval is 100,000 miles for normal vehicle use, and 75,000 miles for vehicles driven under Severe Driving Conditions.