99 Transmission slipping problems

[KR1]

at 75K I changed my transmission fluid/filter, and about 5k later, major slipping between 3rd and 4th. I replaced the ATF with the type recommended on the dipstick (dont remember which kind now, I think Mercon V).

1,2 are fine, but half way through 3rd (at any speed), the transmission slips (???), the RPM drop is 50% of a normal shift, for 1 sec. then creeps up under constant gas pedel.

It reminds me of a manual tranny, when you start to disengage the clutch, and the RPM start to climb, then pulling you foot off the clutch until the RPMs return to the rate of increase.

I recently added some seafoam tranny cleaner, and it seemed to help some