The disks distorting would suggest that the brakes have been staying on, especially if you don't normally use them hard. Try the temperature test.
The intermittent sudden power boost (with clean egr valve) sounds like sticking turbo vanes. Injector cleaner and harder driving cured mine, or try an in-tank turbo cleaner. I don't think this would affect the consumption very much. It might be a split in one of the small vacuum pipes that the VNT actuator relies on. In this case you might be cruising at 120 kph with less boost than you should have, but I can't see it dropping the engine efficiency by so much.
If the brake temperature test proves negative, go back to the manual throttle test, and MES VNT test. What I'm thinking with this last one is that if, say, someone has left a rag in the lower boost pipe when working on the turbo, it will now be blocking the intercooler. The turbo will have to work harder to make the boost the ecu wants so the VNT demand will be higher than normal. Similarly, if the exhaust is restricted, the ecu will have to close the VNT more to achieve the desired boost. In either case the engine is working against higher back pressure so consumption rises. Split vacuum pipes would confuse this test, so you need to check them first.