I am on the "don't do anything to the tranny ever" team now. Same story, had it serviced at Isuzu dealership at 100K miles, <1000 miles later, tranny was toast. I am just letting it go. Worst case, it goes another 100K miles before I replace it again, versus the get it serviced and go 1000 miles plan. I don't know of any tricks for your symptoms, I would just drive it till it stops shifting at all