What can be the problem with my Silverado?

I have an 06 silverado 5.3 Flex Fuel with a cold air intake. i just recently installed long tube headers with straight back true duals 3" piping into super 44 flowmasters and i kept my stock cats. I lost a big amount of torque i used to be able to spin my tires by stepping on it on first gear now i have no torque and i just go without and wheels spinning and no power i also noticed at around 70(4th gear) my truck just stops going anywhere. My check engine light also comes on the code is for the mass air flow sensor. Can it be A.) piping too big B.)Should Install a X pipe to fix it(how should i fix it if its piping issue) C.) I just need my ECU/ECM tuned? Thanks for reading..............Why is back pressure needed?