I tow a large trailer on a regular basis with my DSE ...I carry massive bags of cement and scaffold ...Just stick it in low range and in a low gear ...Its just basic sense.
If they have just been fitted and its a diesel the guy probally did not tell you that they need to be activated via software ...Go to a local landrover expert and tell him/her the story ...Probally just need to be activated.
If you have a problem with the gearbox overheating just attach a tube to the inside of the grill on the bumper and aim the exit at the radiator ...Problem solved.
Nice chocie! I got a 98 DSE ......Don't mess with the engine ...Just do the normal things like check for water and brake fluid ...Have fun with your rangie ...Amazing landrover.