Transmission Slipping?

Chrysler '96 Cirrus I have a major issue When the car hits 60 it misses a gear the whole car lurches and then it will decelerate until it hits 40 then it hits 4-6k rpm when it hits around 50 mph. We found a slight fix where if we drop it to 30 it will downshift and if we don't go to 60 again it won't... show more Chrysler '96 Cirrus

I have a major issue
When the car hits 60 it misses a gear the whole car lurches and then it will decelerate until it hits 40 then it hits 4-6k rpm when it hits around 50 mph.
We found a slight fix where if we drop it to 30 it will downshift and if we don't go to 60 again it won't really have an issue. The car smells horrible after it happens too. If we turn the car off for approx 5 minutes it will completely fix itself no smell no anything as long as we don't hit 60 mph.
The main issue when it does this is we burn through gas like crazy. When it does do this we will burn through a half a tank just going 25 miles in and 25 miles back.
We took it to a garage and they said they fixed it. They flushed the system and charged us $400 and the problem still persists.... does anyone have an idea?
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