Chevrolet Silverado Power Reduced Light

Hello I Bought This Car In February, Had It For A Week And In Shop, Got It Out A Week Later And Drove It, Check Engine Light Came On With...

When I'm Driving It's Like I Take My Foot Off The Gas And The Reduced Engine Speed Comes On

I Did A Ls Swap Into My Truck Listed Above 1500. I Got It To Start, Then I Gave It Gas Then I Saw A Message Reading Engine Power Reduce. I...