x5 slips/jerks in 5th gear at 30-40 miles speed

[kashmir]

After putting a new motor(N62) in my 2005 x5 4.4 recently , I have noticed that transmission slips/jerks in 5th gear at 30-40 mils speed. I had the dealer look into this but was told transmission was fine. it happens frequently and consistently at the speeds i mentioned above. So i am sure the tech didnt really look into this carefully or is just blowing me off!

I didnt have this issue until they put the new engine. could they have messed up the transmission while installing the motor? Could it be from something other than transmission. BTW, I noticed lines coming from the engine not connected to anything? it that normal? did not see notice that with old motor.

thanks