Filament Slipping

I know this has been discussed, and I have read several posts on this subject, but I just can not keep my printer filament from slipping. I have tried adjusting the tension, cleaning the extruder gear and bearing, and cleaning the nozzle. I completely replaced the nozzle and barrel due to a mistake I made. I thought the slippage was due to a clog, but since I replaced the barrel and nozzle, it is still slipping some...any ideas would be appreciated...