Sorry to hear your Flex is acting up! it could indeed be plugs or MAP sensors. Changing the plugs, inspecting the old plugs' condition is a great first step. Never hurts to clean the MAP. Add an OBD II adapter and Torque Pro software, and you can monitor a lot of valuable parameters.
The MAP sensors are circled

the blue is a 3-bar, the yellow is a 2-bar stock. The yellow one is the one you swap out to 3bar when you upgrade for a tune.
Could also be an O2 sensor or a fuel injector issue. Let's hope not an injector.
Finally, is this only on the current tank of gas?