Poor running p38 v 4.0

Hi I have a problem.O n the last two fuel fill up's the car was running fine until I put fuel in then as soon as I left the forecourt there was a lack of power and back firing it is still doing it now after 15 miles, The filler cap seems ok,it revs fine with no back firing when in N ,any ideas?My wife says dirty fuel but as I used 2 differant station I think not.Any Ideas please

Fuel starvation? Check fuel pump and filter.

Have you had it serviced? If so could be a vacuum pipe pulled out

Thanks for your help.I think I have found the problem.I have been putting the filler cap back on to tight stopping the tank from venting.I found that after the three clicks on the cap you then turn the cap anticlock wise that will open the breather vents so the tank can breath,fully closing the cap closes the vents result poor running.and back firing.