Yes, I've read the manual, and it actually says
(under the severe driving conditions section on page 8-11):
*Change automatic transmission fluid every 20,000 miles
*Contact your Isuzu dealer for further informations.
So, that's what I did. I called for further informations
I believe I called Isuzu corporate (not a dealer), and they are the ones who told me it doesn't need to be changed, especially since I don't meet any of the very specific criteria listed on page 8-11 for severe driving conditions. So I should have a case for not having to follow that instruction anyhow. Stupid me for not recording the phone conversation. Hind-sight is 20/20 as they say.
Furthermore, on page 8-10 it says to CHECK (not CHANGE as it says for other fluids) TOD system fluid level every 12 months or every 15k miles. This is what I've been doing. Changing the fluid required special connections at the radiator and a flush machine (from what the dealers were telling me)
So, far as I know, I've been following the book and my warranty shouldn't be void.
And yes, I'm the original owner.
What I was asking you guys is if you think black fluid is enough of an indicator to justify my making a case for the dealer to drop the pan and inspect for damage.
Thanks,
-Mike