The vibration problems normally start when you've corrected the caster angle on the front axle. When you lift the suspension then this puts the caster angle out and makes the steering lighter and it will tend to "tram line" on the road.
The caster correction radius arms bring the steering back to normal but increase the angle of the front propshaft to the transfer box. This increased angle sets up a vibration.
I've had a 2" lift on an old Rangie with no problems running 31x10.5R15 tyres. On the Disco I have now, the 2" lift was okay but when I put a 3" lift & 33x12.5R15 tyres on it then the caster angle needed correcting and the tyres reduced the gearing so much that I ended up putting a 1.41 ratio transfer box in so I could do over 60mph and maintain speed up hill.
If you're happy with the setup you have and you've not got any problems then stick with that. You shouldn't have anything to worry about.