Recently been concerned about a carbon monoxide leak in my pick-up. Recently after a 3-hour interstate drive, I stopped and did a carboxyhemoglobin blood test, the results came back at 2.3 %. I felt that was on the high side of normal, so I took it to another exhaust place, he claimed it had a small leak, and repaired it. so this past week we took it on another 3 hour drive. This time my wife and I both tested again, mine came back at 2.2 and the wifes at 2.8 %. Is this normal after driving this distance or should I be concerned?