Super Custom 3.0td manual vibration

I have at  3.0td manual 4wd here in Christchurch New Zealand. It's a 1996 model I bought imported from Japan with only 68,000 km a couple of years ago. It's like new inside and goes brilliantly.

I use it for my garden design and planting business, so often tow a trailer with it.

I have noticed over the last few weeks a vibration at low revs. Anything under 1900rpm and the vibration is quite strong, as soon as we're over 2100rpm it goes away. If I dip the clutch it goes away too.

There is also a bit of resistance going from 3rd to 2nd gear.

I wonder if I worn the clutch out towing over the big hills we have round here. There's never a big weight on there, but I guess it adds to the wear over time. Are these fitted with a dual mass flywheel?

Thanks for any advice anyone can offer...