Cooperspies, I checked your website and therefore I'm going to guess your pies are formed pies (like pasties) rather than made in pans, correct?
Without giving away any proprietary recipes, perhaps you can give us an idea of the consistency of the gravy/sauce, and what the character of the pastry is: how short is it; what type (how "strong") the flour is. That type of information might help the professionals answer better.
But I'm a home cook. When I have troubles like that, I'd think it could be one of these problems. First, I see if the gravy/sauce was too thin, and therefore has too much steam to give off. I'd also see if the veggies are too wet. If you par-cook them, they'll be drier and give you less moisture to need to escape. Perhaps the ratio of solids to sauce is off (too much sauce?). Or the position of the pans in the oven doesn't allow good heat circulation? Maybe the oven is too hot? Too cool? Isn't convection, but should be? Is convection but shouldn't be?? Those are the kinds of thing a professional could answer, but I could not.
My own chicken pot pie filling is very dense. I don't have a food cost budget to meet as you do, so I can do as I please! But if I'm a bit short of cooked chicken, I use a lot more vegetables and make them smaller. If I have a bit too little filling and some extra sauce, I add a par-cooked starchy-type baking potato cut into dice to help thicken the sauce as it cooks. The larger total surface of the smaller cut vegetables seems to hang onto more sauce/gravy, keeping the sauce from running as much when I cut into the pie. I use a 9" glass pie pan, placed on a metal baking sheet in the lower third of the oven at 400F. It's a double-crust pie, using either home made pastry with margarine or the pre-made supermarket type made with lard if I'm desperate. I use just enough sauce to bind the ingredients with little dripping when I put it into the crust. I've not had crust blow-outs from the edges of the pie, and not a lot of sauce bubbling out through the four vents I cut in the top, center crust either.
I hope the members here can help. I know this is a very important issue for your business.