Our RRS (TDV6 HSE) developed a stutter / shudder on load (seemed to be in 3rd with in D). We got the all the transmission oils (gear box, transfer, difs) changed and so far this seems to have cured it.

We do some (once a month for say 600miles) towing of a 1300kg race car and large brian james TB trailer. So easy 2+ ton.

Can any one give some tips on how to use the gearbox when towing? I've heard its best to use it in Manual mode when setting off.

For example M1, M2, M3 then into D. Or would it just be best to stick it in Manual for all the towing?

With that much weight behind it might even be better to start in low ratio to get it moving, manually shifting L1/L2/L3 - H2/H3 then automatic high box once you are happy - you can change between low and high box when the car is in motion up to 15mph, just do it on the flat not going down a hill! It will use the low box like crawler ratios on a big truck. Manual Low first is also good for controlling the rig on a steep downhill using the engine braking 2020 Pangea Green 1st Edition D240 New Defender 110 is here and loving it
2018 Melting Silver Mini Countryman PHEV - soon to be replaced
2015MY Corris Grey SDv6 HSE Dynamic, the best car I have ever owned, totally reliable only a cou0le of rattles in 3 years, now no longer in my care
Also in my garage is a 1996 TDi300 Defender 90 County HT made into a fake CSW

I regularly used to tow an industrial twin axle trailer with a RR classic on top in auto with no probs at all, only used low when manoeuvring