Fuel problem?

[HONEYMON57ER]

My '99 996 has just started playing up.
Here's the symptom:
Loss of revs for between 3-5 secs in any gear
then kicks back in
No warning lights on
Engine sounds normal
Oil pressure normal
This seems like intermitant fuel starvation.
Coincidentaly I have just filled with BP standard
unleaded 95 Ron but usually use Shell V Power stuff.
Any ideas?

Cheers, Barry