I am having trouble with my 1998 toyota 4 runner SR5 transmission. I have a 3.4 liter v6 engine and an automatic transmission. I have changed the fluid twice now and all the sudden the transmission is acting up. I have gone 5k miles or more since the last fluid change. The transmission seems to be bucking or surging when you are cruising along at 45 mph roughly. I believe that the torque converter clutch is slipping, but not positive. now the problem is getting worse and it seems to be doin it whenever it feels like it whether the od is on or off. has anyone experianced this problem before.. please help.
Thanks :)

Did you get a good look at the filter?
If it is blocked it can cause this. It seems too coincidental that it would start right you changed the oil, or was that the reason for changing the oil?

Do a search in this forum for transmission: shaking or lurching bucking shuttering there have been posts on this.
Good luck