Well its very possible that its an ignition problem, there are several other problems it could be, but my first line of investigation would be ignition. Doubt it will just be plugs though, need to get your mechanic to check them out but also the condition of you HT leads. Next is determining if your coil packs are kaput and then the PTU. Its handy to have a friendly GTO uk person come with a working set to swap yours out to see if that's the issue. Firstly though a visual inspection of yours should give you an idea as to their age, if your coil packs are rusted and the plastic is perished chances are they've been on there since 1991.
Lack of fuel pressure was a problem with my vehicle and that manifested itself in occasional poor idling and loss of power. Do you have any poor idling? after the vehicle warms up / goes for a drive, perhaps on restarting the vehicle? or not driving much to assess?
Anyway Start with ignition. However for future, I would recommend getting rid of the old pump and in with a new one! also a FPR that raises fuel pressure in line with fuel demand is useful for future 'tune ups'
Other things to consider is perhaps a timing issue, when was the last time the belt was changed? Or potentially a failing MAF however I would suspect an engine management light to throw up if that was the case.
Let me know what happens and if you need me and some of my parts for testing let me know and I will venture fourth to your locale and apply my particular lack of skills and logic to your situation.