My 03 starts and sounds great like a straight pipe should then when I start to drive it it goes to a loud whistle and decrease in power and misses sometimes if u floor it otherwise no problems and doesn't run any codes

 

Is your turbo clean inside? If vanes stick it can run bad!

 

Agreed! The turbo vanes need cleaning every once in a while. Too much soot build-up will make them stick, and poor performance is the result. Also if its missing, it may be caused by foaming in the engine oil. The injectors are fired by high oil pressure, and foamed up oil will cause misfires. Try another brand of Engine oil. Good luck!

 

Ok I'll change my oil and see how that works as for cleaning the turbo I've never done that don't really know how to either I've always owned a 7.3 just bought this truck