Hi had very similar problem, mine felt like it was pinking / running out of fuel, eml came on chuffed spluttered and died, got it home on a truck, cos its auto, dammed thing started but refused to start at side of mway, hence ride home, break down chap had no idea, got a mate to run diagnostics on it and it came back p1020 electronic speed govenor ! could not find out what that was, scan done with a snap on solus pro, all faults cleared and the blasted thing started after a couple of turns, doing a live data check it spluttered to a holt whilst ticking over, it had been running for about 3/4 mins only, checked again same fault, sod it left the pig for over a week till i found out more info, but nothing doing, then got told the solenoid on the pump could give problems and take it off clean it or replace it cost new about ÂŁ70.00. whilst it was ticking over pump preasure was measured and it read 350 bar and whent to 800 when revved, so was told pump fine, no miss fire and after turning on and off each injector as you can with the snap on gizzmo you could feel the effects as each one in turn was off, so nearly took solenoid off and nearly bought a new one, untill anoth mate came over after hearing my woes, He looked at the pump and ran a few checks cos it started again and ran for a while temp guage at normal and revving it up now and again, he said pump fine have you checked the fuel filter after looking at it cos it looked newish, he removed the pipes and unbolted it, why ? well he said he was looking for a sqished pipe or other blockage, but said he though it was fuel starvation rather than any other fault, he had a gadget to test the flow from and back to the tank after looking at fuel gauge he suggested whilst it was still in a running state i go and get 2 galls of fuel whilst he put filter etc back on, filling station 2 mins away on returning with half a 5 gallon drum of the liquid gold we removed the filler cap, and behold a hissing noise but not from preasure but vacume! was yours the same ? sucking rather than blowing, we filled the tank and just as an experiment left the cap loose I usually tighten it till it clicks, the reasoning was that it could be a breather problem ! We ran the car again after pumping up fuel through the filter it started no problem we ran it for a good half hour outside my house with live data and all sorts of other checks being done, we eventually decided that it was time to take to the highway, after making sure we had the means to get the car home should it turn out to be a red herring, belive me I was at my wits end thinking pump injectors the cost was going up to the point that scrapping it looked good, We took it out drove it around town up hill down dale and along the bypass, it performed like a good un all live data at hand to boot in case it did throw a wobbler, next we took it on the mway, risky I know cos were getting further away from aid if we need it, but mway it was, clog down 70 all the way odd spurt up to a bit more like you do, slow down to 40 ish hit some good hills cos we have them , long steep drags start off at 35 and boot it up the hill make it work and use a lot of fuel, gear changes slick power loads of it quiet smooth everything youd expect not a bloody murmer from it, and so far so good, now I am not saying this is the answer to your problem just that it seems to have been the answer to mine, as a result I drilled a 4mm hole in the cap to aid with the venting in case it is a blocked vent just though I would share this with you in case it helps cheers and good luck hope you find a cure....