this is a classic symptom of a failing alternator on the isuzu. (or a big box cheap 'rebuild' unit even if 'new').
you probably would have gotten more replies about this except your initial post got us sidetracked to relay info. all sorts of weird dash light happenings occur when the alternator starts going bad (even trans problems will surface because of defective alternator).

generally, most will tell you to stick to quality alternator alternatives...in descending order of $, but all should be good
*dealer new
*dealer remanufactured
*remanufactured by bosch (my personal favorite from experience)

avoid:avoid:avoid::cheapo rebuilds from bigbox parts stores. if they say "lifetime warranty" be afraid, be very afraid. it means a lifetime of replacing them.

hth

//bc