L322 hanging in third gear(plus a bus noise)

hi guys my l322 3.0td6 2005 has a new fault it drives fine then does not want to change to 4th gear unless take foot off and back on agin about 4500rpm no fault codes stored. gear box had full over haul 4 years ago... heard a few things but dont want to try them untill talked to you lot... eg reset trans ecu.. but can cause more probs at this age.. also my not be the same thing but after being in traffic for 15 mins stop start driving it sounds like a bus moving off and only way to stop it is to floor it for 5secs ish... and it dont matter if i am in park same sound...


with thanks guys...

Are the sure the noise in stop traffic is not the viscous fan on the engine working.

i belive it is mate but the way it sounds something must be wrong even with the fan.... but i dont know what?