My trusty dual-fuel wagon had this problem, same on gas or petrol, so I'm thinking ignition. It's not driveshafts because it instantly goes away when it downchanges, it only happens on light loads, slight uphill, 60-65 kph, top gear (4 speed auto). So I had it serviced at the local dealer, they changed air filter and plugs, checked the distributer cap, which they said was OK, but it still does it.

Any thoughts? suggestions? maybe HT leads?

I've had the same thing happening with my TH 4 speed auto for over 100,000 kms. I was told it was the clutch (forget exactly what they said) in the gearbox.

Possibly engine mounts?

Mine does something like this occasionally uphills in 3rd (4sp auto) - has a slight shake upfront like it wants to go to 4th but then theres a vibration, you back off it goes, or if you give more pedal and it goes into second it disappears. I have heard it make a squeaking noise when its done it before, nothing like slipping-belt noise, its like a metal on metal s-s-s-s-squeak. Not like engine or auto internals doing it, its un-muffled like its in the open, not within the confines of the block/auto/bellhousing) but I can't "see" the if it's indeed a damaged engine mount.

engine mounts? I didn't think of that. Are they hard and/or expensive to replace? I have to say, it really feels like an ignition misfiring problem. But, if I had a $ for every time I've been wrong.............

How many k's has it done?

The problem is that in top gear, you're only doing like 1,000rpm at 60kmh. That's pretty much as low as you can go without changing back a gear. When you're driving along flat road you wont notice it because there isnt much load on the engine, but when going uphill there is more strain. My 380 does it in 4th and 5th at such low revs, and my old TJ did the exact same thing in 4th. Just change into third if it annoys you.

Generally this is the lock up clutches in the torque converter, had an AWD here the other day with the same thing, only 60k on the clock, the customer went to my trans specialist who added a special treatment designed to clean off the torque converter lock up clutch can eliminate the shudder, he added this and in about a day or so of driving the shudder is all but gone. May be an idea to try this IF the issue is in top gear

If in lower gear, ignore above lol

Generally this is the lock up clutches in the torque converter, had an AWD here the other day with the same thing, only 60k on the clock, the customer went to my trans specialist who added a special treatment designed to clean off the torque converter lock up clutch can eliminate the shudder, he added this and in about a day or so of driving the shudder is all but gone. May be an idea to try this IF the issue is in top gear

If in lower gear, ignore above lol

It's done 72 k. re the earlier post about it being a low engine speed in top gear etc, yes, I know but it's a relatively new thing, only in the last year. Problem occurs only in top gear. I'll call my local trans guy and ask if he has the product, thanks Mal.

Generally this is the lock up clutches in the torque converter, had an AWD here the other day with the same thing, only 60k on the clock, the customer went to my trans specialist who added a special treatment designed to clean off the torque converter lock up clutch can eliminate the shudder, he added this and in about a day or so of driving the shudder is all but gone. May be an idea to try this IF the issue is in top gear

If in lower gear, ignore above lol

do you know what the product is?

I've thought some more about this (I know, it takes me a while) and I've decided that I'll get the fluid drained and replaced with genuine mitsi fluid before I do anything more.

rang my trans guy, he said, just try a re-learn first, guess what, problem seems fixed. Touch wood, hope it stays away. definitely has changed it for the better.