It depends on the condition of the vehicle. If it is well maintained, cooling system is in good order, a 2.8 auto should not have a problem in cruising at 120 on motorways. However, the speed needs to be reduced on inclines. Most pajero experts recommend keeping the rpm below 3000 while cruising. If you want further safety, get an EGT gauge installed. You should be aware that a 20-25 yrs old vehicle will require periodic maintenance.