This is indeed an unfortunate problem and $2700 is not an insignificant unexpected expense these days.
But I agree with Trav. More to it than a simple fluid problem or incompatibility issues with ML. And I have seen the exact same thing happen with the filter Trav described, and, yes, it could kill a trans in short order, though the adverse drivability symptoms would like come right away. This "new fluid kills old automatics" thing is almost pure myth. We could have a very long side discussion on that.
Sometimes it really is just a case of "fecal matter occurs." Trannies just die and if they are going to die unexpectedly, old Murph usually dictates the most inconvenient time. An unbaised and expert autopsy could yield the true cause but that might be difficult to arrange and prohibitively expensive.
I will also vote with Trav on the efficacy of cooler line fluid exchanges, when possible. After a first pan drop, that is.
My studies have yielded the facts that the average automatic produces some 75 percent of it's lifetime amount of contaminants in the first 5K of operations (25 years of studies by Eleftherakis & Khalil), which is a combination of what was built in by residual mfr. debris and break-in wear. This makes the first fluid change/pan drop the most important and best done early. After that, an easily used trans does not create much contamination and it's just a matter of gauging fluid life... which is often very long in an easily used trans.
To go farther with this and explain why that first change is so important, John Eleftherakis and Abe Khalil, who have done a series of studies for the OE trans manufacturers and the aftermarket that started in the late '80s, and continues to today. After sampling the oil in thousands of automatics in service, they found that the average trans with 70K or more miles that has not had a service contains approximately 263 mg/l (milligrams per liter) of contaminants, 90 percent of which is metallic. Of those metallic particles, 51 percent are ferrous (iron/steel), 21 percent copper, 11 percent aluminum and 7 percent lead. The particles range in size from 5 to 80 microns, about 82 percent of them larger than 5 microns. Yes the trans has a internal filter, but the best on the market today filters at 80 microns nominal and many cheap ones, or older filters are at 100 microns, or larger. Some of the screens in older transmissions are 150-200 microns and all they get are the "boulders.
Long term, the metallic particles cause wear on the pump vanes/housing and on bearings and bushings, but valves don't like debris either and that's where the shorter term problems can come from. A chunk of debris can score the bore of a valve and cause it to leak, or jam outright. I don't have to tell you what a metallic particle will do to a rubber seal or o-ring, or that a chunk of iron is a lot harder than an aluminum valve bore.
With the advent of electronic valves, a new problem was created. What is an electronically controlled valve?? An electromagnet! Magnets attract ferrous particles, so the iron in the trans is gravitating to those areas and causing valve malfunctions to occur even sooner. Once the valves start to malfunction, you get reduced pressures or delayed shifts, all of which cause extra wear on the clutches. Often it's so slow and imperceptible that the driver doesn't feel it until it gets really bad. That might be at 100K miles, so he says, "Oh well" and has the trans rebuilt when, with some care, that trans might have outlasted the car. Sometimes there is so much manufacturing grunge (or remanufacturing... rebuilt trans have the same trouble) in the trans that it fails under warranty.
This could also be a good argument for additional trans filtration and this is an increasingly common feature on automatics.
The good news is that, after decades of ignoring the problem, the OEs are finally instituting some manufacturing upgrades that should eliminate most of the built in contamination. Improved internal filtration has been developed as well ( there are some design hurdles that have limited the possible efficiency of a pan filter). Unfortunately, Oil Changer, the 4L60E in your Astro doesn't fit into that "new age."
If you plan of keeping your Astro long term, a cooler line filter is a good idea.