This is the reason I went with APR. They really do alot of research and testing to make sure there product is perfect before they release it. Take your time. I know peolpe on here don't want to wait, but I do.
Fuel trim issues and misfires point to mechanical problems with your car. You need to get them diagnosed and repaired. Fuel trim problems usually indicate a problem with the intake, maf, or a boost leak. Misfires are an ignition problem or weak valve springs. Apr has a tune to compensate for bad exhaust springs. You probably need to replace your plugs and coil packs. You need to vagcom and get the issues fixed a tune can only mask the problems not fix them