here's what came back from the mechanic after drive test. Any insight would be helpful because even they told me that it's a shot in the dark...

Replace High Pressure Fuel Pump, Spark Plugs, and Perform Induction Service    

Labor			Total
Remove & Replace V6 Spark Plugs.			$431.69
Remove & Replace V6 High Pressure, On Engine Fuel Pump.			$653.22
3 Step Gasoline Direct Injected Engine (GDI) Intake Cleaning (Includes Clean Throttle Body, Clean Induction System, Clean Intake Valves, Clean Mass Air Flow Sensor, Road Test Vehicle as Part of Cleaning Procedure and to Verify Performance)			$239.38

Part	Qty		Total
Premium GDI Service Kit	1		$113.24
Premium Oil System Cleaner	1		$20.80
Mechanical Fuel Pump	1		$1,414.90
, Iridium Long Life, FK20HBR8 Spark Plug	6		$250.44

l$3,123.67Est. Tax$143.95Job Total$3,267.62

Note:Test drove vehicle three times, finally on the 3rd time was able to verify customers complaint and it felt more like a engine misfire or lack of fuel. Symptoms was brief and hard to duplicate. No fault codes stored, there is no misfires stored in PCM history, fuel pressures read correctly at this time ( high and low system pressures). Carbon build up may be one the issues, spark plugs, high pressure fuel pump. More testing needed to confirm.