Thanks for all the suggestions thus far and I have chased all of them to dead ends. I am starting to think more definitively it is a gearbox issue.

All gears are solid and definite without any resistance or slipping out. Even the 5th is solid and smooth without any issues. This gearbox has been a stellar performer since day one, 000,256kM till today 332,980! No Issues!

But suddenly last fall when climbing a fairly steep incline through several turns I heard growling and felt a slight loss of torque (juddering?). Since then I have learned not to accelerate into that "bad zone" where it growls and I just follow the torque curve to stay just shy of the growl when I am in a situation when it has the potential of appearing - hills and hard acceleration. But poor first gear receives a brief exposure to the growl and vibration when setting off every stop. In first, second, and third this initial growl passes if I let off the accelerator a bit, then it is unnoticeable unless I step into it. 4th and 5th gears do not indicate any growl or vibration but that may just be the lower torque they are exposed to. (Sorry to bore you with this repetitive description)

I have just had the clutch replaced, resurfaced the flywheel, and replaced both transaxle's and their built-in CV's. In fact, just about everything suspicious of vibration has been replaced - including all the engine and tranny mounts.

I'm headed towards replacing the gearbox. Does everyone agree this is the next logical direction?

1. I am concerned about getting a gearbox that has the dreaded 5th gear issue. Any thoughts as to why I have never experienced this issue?

2. I cannot for the life of me find my gearbox part stamp? Does anyone know where I may find this? Alternatively, given the data below can anyone tell me with certainty what gearbox I do have?

3. Has anyone had luck with a refurbished gearbox exchange?

Thanks so much for hanging in there with my issue. I have appreciated and heeded all of the excellent suggestions and advice given to me on this forum.

Yes, it's the same vehicle;
N+B Flair Motorhome
4/3/2000 FIAT Ducato 18Q - 2.8 i.d.TD
8140.43
122 PS (90kW;120 hp) @ 3,600 rpm
VIN: ZFA23000005887229
Engine: 3050633

Gearbox OKAY! Still Vibrating Up Hills and When Accelerating!

[/B]Back to the beginning again.

Some kilometers back I posted the dilemma of having this persistent vibration and thought it could be the gearbox. I found a stellar gearbox rebuilder in NL that invited me to let him have a look at my issues. He is a large worldwide distributor of gearboxes and had thousands of rebuilt gearboxes on the shelves and ongoing refurbishing in the shop by what looked like very skilled technicians. Schoones Transmissies BV.

The owner gave my Motorhome a run around the industrial estate and then out onto the motorway and really put it through a thorough test. His judgment was that these transmissions with the stamp 20KM57 are the most heavy-duty and reliable FIAT has ever produced. He also said there were no tranny issues - even after 335,000km! and that I shouldn't expect any for the life of the vehicle. He also refused to take any money from me, there was nothing wrong with my trans.

So back to square one with the vibration issue. Having just replaced just about everything from the CV shafts to the clutch, all 3 engine mounts I am still stumped. Given that everything under there appears tight, I have just kept my acceleration very conservative and keep the torque just below when the vibration begins to appear. Take off at first gear, and second gear if I step into it. Third gear can show the vibration but only if climbing a hill.

This all vaguely seems to have started with the replacement of the left side motor mount (bearing) so I am going to replace it again. But I do wonder if the LH and RH mounts are exactly the same part? The FIAT part number is 1307907080, but the extensions are RH 1827.19 and LH 1827.17 those numbers differ. IF THEY ARE DIFFERENT COULD THE PROBLEM BE THAT I HAVE A RH WHERE THERE SHOULD BE A LH? Inquiring minds want to know before I order another part.

If anyone has any suggestion of the origin of these symptoms or the answer to if these are truly different parts in configuration or manufacture please let me know.

As always thanks for your invaluable advice and input!