If you are fairly mechanical, you could do it yourself. If it is the Vacuum solenoid (for the TOD) I think it was $150 or so from St Charles Isuzu... And if it is the TOD position sensor, I think that was $120 or so from St. Charles Isuzu as well.
Go to
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Follow the links to marketplace and you will see St. Charles Isuzu on there. You can call them up and their prices were wholesale (they were cheaper than the two dealers by me in Wisconsin) and I think they even ship for free.
Don't know how much any of these would be if you had a dealer replace them...The dealer says the solenoid pack is a common fail item (due to the poor sheild and mount design by Isuzu) I would have thought they would have a recall on this by now!!!