Infiniti: Sluggish Starts

Having some issues with my Infiniti J30t. About 25-30 percent of the time
when the vehicle is warm and I start from a dead stop, the car lacks power
big time! Almost feels like the car is in 3rd gear from a start or even
over drive. I have manually downshifted though before to first and still is
sluggish. I have changed the plugs, fuel filter and air filter and still
does it. Doesn't ever seem to do it when it is cold, if that helps narrow
it down. Any suggestions?