OBDII code P1870?????

[race_b51]

I now have the code P1870 which is related to the transmission.......have 1998 chevy truck 305V8 4speed auto tran w/od, I have read previous posts where just changing the fluid and filter, to replacing the tourque conv. to some sort of GM valve in the tranny, to fix this problem. Is this a do it yourself or should I get attempted rape from the dealer or a local tranny shop???? any insight would be much appreciated..........thanks
I do not know when or if the fluid was ever changed, I have 136000miles on the truck and the fluid is reddish brown and does not smell burnt......the truck seems to shift hard and buck like being hit from behind at times, it just started these symptoms and does not do it all the time, especially on short drives........???????????............