loss of throttle when put in gear

When I first start the truck it idles verv low. When i give it fule it sounds as if it is going to flood out
afta few minutes it idles up then the accelerator works fine. But as soon as i put it in to gear i lose all acceleration. I have to hold in clutch or take out gear and play with gas peddle till accelerator begins working again. But it will go out as soon as i put it back in gear.