movano gearbox ratio s?

I have put pfiaa012 in my movano ,a pf1aa013 and the origanal box was a pf1aa014 I would like to put in a high ratio box in my 2.8 as it seems to rev high on the motorway.I have in my possesion a pf1aa017 which i thought was higher but it looks like its the lowest ratio box that you can get. Could you tell me if this is higher or lower than the pf1aa014 that the van came with or what is the highest ratio gearbox i can put in my vauxhall movano? cheers joe.