Also pretty sure a P3 does not include the diff oil change. Lincolnbaggie had a thread up somewhere about how the P2 and P3 are for all intents and purposes identical.
Diff and gearbox oil change is and extra piece of work I think (and not a cheap one at that - circa £100 for both).
Diff oil and gearbox oil don't necessarily need changing - some do for piece of mind, but it's not actually needed on the 350. Fuel filter ditto.
And, yes, the P2 and P3 are identical. OP, Yours needs a P2 this time and possibly coolant and brake fluid depending on when these were last done (brake fluid should be every two years and coolant every three years regardless of mileage). Also, technically your plugs should be changed after 5 years, but most do them around 45000 miles.
Westway Nissan are wrong - second P3 should be at 8 years (72,000 miles) and is pointless anyway as its the same as a P2.