Poor accelerator repsonse

Car starts on the button and idles perfectly from cold. When pulling away the rpm's fade and there is poor response from the accelerator. The clutch and accelerator need to be managed to keep the car moving otherwise the car will kangaroo until warm. Once warm car is fine until >3500 rpm when the car will hold back with the occasionally misfire......Car has been serviced, throttle sensor changed and coil pack replaced....diagnostic analasys reveals for obvious problems...garage is at a loss can any one offer advice...PLEASE!