I have a 99 Honda Odyssey EX with 133K mi & the transmission makes a loud thud when upshifting from D1 to D2.?

During the upshift, the tach revs up from 2K RPM to about 4K RPM as if it was on neutral or park for about 1 second then goes into D2 (while the van is accelarating). The same happens when it upshifts to D3 but not too noticeable to D4. Is getting a used low mileage transmission worth or is it still repairable ? And what does the repair manual mean when it says "flaring"? Thanks.