Hay mate, sorry to hear you are still having issues.
From your first post
And your last postQuote:
On arriving home thinking it could be a transmission problem I took it to my guy to check out he could not find any problems so suggested it was an engine fault.
.Quote:
now advise me the problem is the transmission and nothing to do with their work,
Sounds like you are being given the run around. As @Bidja suggests, it sound like a boost problem. I have the same motor and gearbox and monitor my water temp and gearbox temp with aftermarket guages. The closest I have had to your symptoms is pulling a fully loaded camper trailer up a large long hill here at Collie in WA. I hit 120deg water and 90 deg gearbox and was unable to exceed 40K to get over the top. It turned out to be the viscous hub and partially blocked radiator. Swapped the lot out, including water oump and all perfect now. The point I am trying to make is that there is gearbox cooling in the radiator and if the cooling system is not performing properly it can effect the transmission, in fact can kill it if you burn the transmission fluid. Anyway it sounds like a vacuum or boost leak to me and maybe not a transmission issue. It only takes a very small vacuum or boost leak to throw the entire system out a wack. make sure the transmission mechanics have a good reputation and get a written assesment if you can. Same for engine mechs. You shoudnt have to continually pay for new seals and things for no result.
Good luck with it mate and hopefully you are back to noemal for Christmas. Keep us informed of progress plaese