As has already been said, the POH should cover it and if it says you can (using the correct calculations) then you can.
The insructors I had in Nelspruit (2900amsl) and Jo'burg sounded a bit like Estate Agents with a different mantra - "lean, lean, lean" particularly not allowing yourself to get "hassled" by ATC whilst lining up and leaning yet again.
The guys at Lanseria were not at all keen on people having more than two up in a 172 and the one I flew in FANS felt a bit sleepy with three of us so be careful about the weight.