Every now and then, it kicks out a 137 and 157 code for low voltage on the O2 sensors. It only does it after a long WOT pull through "passing gear" at speeds over 65-MPH. I've replaced the plugs and both O2 sensors within the last 1,000 miles and it did it again yesterday. Engine seems to run just barely rough enough to cause a familiar vibration throughout the truck, but clears itself up after a while. My wife probably wouldn't notice the vibration, but I do, it feels like a slightly out of round tire or out of balance tire in the seat of your pants. Any ideas on what would cause it to throw this code after a tune-up?