There are no studies that show glutamine supports muscle building because thats not what its inteded to do. Its intended use is to preserve/protect muscle from breakdown.

And muscle-milk isnt a weight gainer, its just a protein mixture. A damn good tasting one at that, but its pricey. Although I'm sure the company that makes muscle milk, Cytosport, makes a weight gainer.

That's semantics since net muslce gain is the difference between protein lost and protein gained. Plus there are not really any studies that prove glutamine improves muscle retention in healthy trained individuals. Unless you use it intraveneously or compare it to placebo. Protein in general will help preserve muslce.