I had a K&N filter in the stock box of my red truck before I bought the K&N FIPK, and the filter oil fouled my MAF sensor. I know most are probably thinking I over oiled it, nope. That was straight out of the box. Luckily the MAF came back to life with some cleaning. After that I bought the K&N FIPK intake with the thought that maybe that setup was different enough to keep the MAF isolated from the filter oil splatters. It wasn't, same thing happened again. I put a dry Amsoil EA filter on the FIPK and never had that issue again.
All this was enough to ensure that I never use an oiled gauze air filter on a vehicle with a MAF again. Back to ACDelco dry paper filters for me.
On that note, there are two different sizes of filter that fit in the factory Vortec box. The standard size, and a larger high capacity (K47) one. The ACDelco part number for the larger high capacity paper filter is A1301C.