Yes those still exist however they more commonly advertise their wares on Forums, Fizzbook and other places these days.
The adverts you see depending on being able to manipulate the fuel/air mixture on a turbo car which gives MUCH more option to tweak quickly. For Fuel Injection engines it is a little more difficult. In/Out and engine map will give a little, camshafts might give more as well but will require far greater investment than the turbo engines. The issue with changing the cams on the engine is that they are already pretty fancy on the later 4.8 engine with it's dual VANOS engineering?
A set of racing cats, a good inlet filter and a big exhaust may give you a bump. A remap of the fuel management ditto but trying to find someone with intimate knowledge of that on the V8 will be quite rare I suspect.
Aero Racing do the exhaust, cats and may know more.
