Ok, thanks for the advice thus far... so I replaced the in tank pump and there was a slight improvement in up hill grunt, but not a lot and the original problem still persists. Off the mark sometimes I get boost, most of the times its flat as a pancake. Going up hills is fine up to a point and then the boost just drops off and its back to 10j performance. Take foot of pedal and reapply and it usually comes back on boost for a short while (10 - 20 seconds) before dropping off again. So started thinking perhaps it was gulping air into the fuel sysytem somewhere... checked the fuel filter seal, it's fine and working as it should. No obvious bubbles in clear lines, leaks or wet patches when left running on the drive for an hour.
Last night got right pi$$3d off with it and pulled over and jammed the binoculars box between the pedals to hold it at 2500rpm while I checked the pipes over yet again... First off I noticed that the leakoff pipes are 'thumping' particularly hard when held between finger and thumb, most noticeable across cylinders 3 & 4. I pulled the leak off pipes and they are dry, not a drop of fuel in them at either 2500rpm or on tickover? She has been returning pathetic MPG since the problem occured, averaging 14mpg over the last few weeks, so I reccon that there's no fuel going back to the tank, but like I said, there are no discernable leaks and the oil level isn't rising noticeably over the passed 2 weeks despite daily checks for fear of the rings needing replaced... any ideas would be great, because its almost like a fuel sucking vampire is sucking the life and fuel right outta her before flying off without a trace :? I would really appreciate some further guidance, because she is costing me about £0.70 per mile at the moment and she's my daily works truck. Thanks guys.