took my car for a spin yesterday, hammered on it a little and when i got to the store i noticied a high idle about 2500 rpms and the idle sounded different not like it wAs missing, got back on the road and had no power at all , took it easy back to the house and piddle a little bit with it it revs up good just high idle and no power and this is a fresh built 408 just got from tuner few weeks ago any ideas????

 

A log would at least give some idea. Could be fueling, knock retard, valve issues, TB, vacuum leak. . .

 

High idle indicates vacuum leak possibly. No power could be a fueling issue...the car could be in limp mode. Are the Fans running even when cold?

 

What gauges do you have? Can you read manifold vac, fuel pressure, and AFR?

I'd check vac lines first if it drove home fine from tuner. Look for cracked lines and loose connections.