Wow! I have to wonder how you escaped serious problems with all that extra transmission fluid. Just a quart extra can cause problems by raising the pressure to a point where deposits can be blasted loose from internal pieces and carried to other areas where they may block up galleries or the filter, causing fluid starvation and all sorts of problems. And that’s only with a single quart.
You VeeDub’s tranny was overfilled by two liters, a huge amount of fluids. It is amazing that deposits were dislodged and blown all over the transmission. And, it’s also even more amazing that the huge amount of pressure didn’t blow out a line or a piece of gasketing, emptying the transmission fluid all over the floor of your garage or driveway.
And, given the fact that nothing overly bad happened when the fluid was withdrawn. Notice I said not overly bad as I suspect there has been some very subtle damage to what sounds like the clutches and bands and, possibly, the clutches, bands and gearing. It is also possible that one of the cooling lines may have been damaged and overlooked when the tranny fluid was withdrawn which is also causing the problem when the transmission is hot. The cooling isn’t adequate any more.
With that said, I’d recommend having your technician look over the transmission again, concentrating on the radiator/cooling lines. And I would also have the clutches, bands and gears checked over for signs of damage or too much wear. I suspect the problem with your transmission is in either of these areas or, possibly both.
It’s really good news and bad news. The good news is that the damage isn’t worse and the bad news is that it will still cost you about $1,800 to have repaired. One other piece of semi-good news is that repairs won’t cost your $3,000-plus. Instead, they will work out to about $1,800 or so.