Clutch Judder?

Had the same 1999 Jimmy from new and hardly ever used 4 WD. A couple of weeks ago the clutch started slipping at around 65K miles. Local trusted garage fitted a 'Blue Print' kit, but as soon as I drove it, I knew there was something wrong. It drives as though the gear rations have changed. Where it was happy in 4th at 30mph along a flat road, there is vibration and the only option is to change down. Same sort of problem with all the gears. Now having to drive it much harder and of course using more petrol. The garage had it back to check mounting etc. and eventually removed the gearbox, all to no avail. Just wondering if anyone else has had a similar problem - it has been suggested that perhaps the springs in the clutch are too strong? Thanks for any help.

Honestly I would say that the old clutch might have been not strong enough allowing the engine to over rev though not quite slipping enough to really notice. The springs can not be too stiff. Their job is to keep the friction plate engaged with the flywheel. If they are too stiff then, being cable operated, the effort to push the pedal would be a lot harder than the previous clutch! The vibration would be possibly that the engine is struggling to pull the gear you have selected. In your title you mentioned clutch judder but your description does not really describe that. Just a thought that's all.

As Mick said from your description you are not describing clutch judder.
Clutch judder is when you pull away and while letting the clutch engage you get the judder.
It does sound like the engine is stalling due to being in too high a gear.
Having said that I would have thought 30mph in 4th gear would be ok if you were just drifting along but if you then want to accelerate the engine doesn't like it.
I used to work nights and coming home early in the morning I could drive mine 10mls all the way home in 5th gear between 30/40 mph over 3 roundabouts as there was no traffic around.
The Jimny is so flexible.
I can't understand why you could do it before and not now??
Maybe give it a bit of time for the clutch to bed in a bit then check the adjustment.

Thanks for the interest. I called it " clutch judder" because that is what the 'Blue Print' tech guy said it was after I emailed them about the problem. Like you, I would not have called it "judder" (which is why the ? is there). When you drive a car for a while, you just know when to change gear. I would have known if it had been slipping and as soon as it did start slipping the clutch was replaced. It has always done about 36 mpg which I would think is about right for how and where it is used and if the clutch had been slipping, then I think that it would have affected mpg. The springs I am talking about are actually on the clutch disc; not the leaf springs on the the pressure plate.

To be clear, there is vibration unless a lower gear is selected from the one that was the correct gear from September 1999 to February 2016. The vibration is there even when de-accelerating. As gilburton said "I can't understand why you could do it before and not now" ! At least the garage manager knows it is a problem and has not tried to fob me off by saying that it is normal and will wear in over time. However, there seems little point in taking it all out again unless we have a good idea of what might be wrong.

When they refitted the gearbox could they have disturbed/damaged the wiring to the low range or 4wd switches on the transfer box ?

Short answer is, I don't know. The 4wd still operates as before. I will mention it to the garage, but how would any damage cause the problem I have described?