I also use the IPAD 3, with an external GPS unit. XGPS150. I had read that at times GPS was unreliable within the I PAD, therefore utilise an external source.
For the first time I experienced this the other day. Flying in a friends aeroplane, I took my IPAD, but not my 150 GPS source.
The I PAD lost position on at least three occasions. It also appeared to lag behind the other GPS units in his craft.
Will always use the external GPS unit from now on, and suggest that for the cost of around 80quid, well worth it.