Check Engine Light means there is problem in the emission control system of your truck. They recommend to retrieve the trouble codes stored in the truck's computer to properly diagnose the problem. For more info about the CEL visit; http://repairpal.com/check-engine-light
I just answered your second question - but clearly, you have an issue with the engine performance on this truck that has clues in the processor that is setting the check engine light. Have the diagnosis performed.