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The MAF could be the source of the problem if it's not giving the car a correct reading. Another member had the problem on his 745 and he disconnected the MAF completely. The car ran STUPID rich but all the drivability and sluggishness was gone. In all honesty, I would buy 2 new MAF sensors and put them in. They should help a LOT, and if not you can return them!
FYI, K&N has been known to mess up sensors because of the oil in their kits! The problem is not the filter nor the oil itself, but the amount of oil that is put on the filters! When people recharge the filters they use WAY to much oil and that can coat components over time.
IMO the best filter design I've seen is on the OEM Honda Filtech filters, they are a 2 stage filter with oil on the bottom half and then paper on the top half. This allow any oil vapor to be caught and allows for superior filtration. The only downside is that they need to be REPLACED every 30K.
Also, one thing you might want to look at is going to an independent mechanic and have them check the FUEL PRESSURE after the HPFP, after the in tank pump and at the filter as well. It could be possible that there is an obstruction of some sort.
Ethanol in the fuel now allows parts to corrode and have build-up accumulate on them! I've gone through 4 fuel sensors because they stop reading properly! I wouldn't be surprised if the same stuff doing that was clogging the lines or doing other sorts of damage.
I've been using Redline SI-1 fuel cleaner RELIGIOUSLY for the last 15K kms (every 5K a full bottle and mini maintenance doses in between) and I've noticed that my car is running a LOT better and as well gives better gas mileage!
One last note, I see that it has 135K kms on it. The spark plugs are supposed to be changed at 100K along with the intake manifold gasket. If the plugs have 135K kms then I wouldn't be surprised if it was the problem! However if they are new, an improper job reinstalling the intake manifold can cause a LOT of problems on the 760 as well!