37,000 miles on car, no increase in rpms, only "slips" for about 1 second.
Between 55-70 mph only, feels like transmission slips. on 2007 Mercury Grand Marquis
If it were slipping rpm would increase, even for that 1 second! Scanner can actually display data to show slippage. Have it tested.
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There is a history of front pump failures on those, hope it's not yours.