E36 auto gearbox trouble

[gazza]

hey guys
i got a E36 323i auto, when it rains my car becomes very sluggish, when i pull off it feels as if its pulling off in 3rd, after about 10meters or so it gears down and then decides to go.
also iv noticed that if i floor it from a standing position, it pulls off as if im driving ms daisy. my old lady has a 323i as well but its a E46, and her car jumps off the mark.
has anyone had problems like this?