Yes it is possible but not common to have neuro symptoms with a 550 reading. In this thread is a copy of Dr. Snow's comments on neurological symptoms with B12 levels that appear normal.

So look back a few pages to that entry.

Vegetarians can be low in other things too. Zinc is one, and so is the amino acid methionine.

However, eating beans and other veggies can give good levels of magnesium.

Potassium however, could be low, and you can be tested for this.
Meat is a main form of potassium in most diets and vegetarians miss that.

I'd get tested for Vit D3. Low levels of this can create problems, and is quite common.

An elevated MCV is often one sign that B12 may be low. But that is not cast in stone either.

You may also want to look at gluten intolerance. This can cause neuro symptoms too. And you may be eating alot of it on your diet.