Have you read this book by Piston? Covers the points you bring up in great detail. Longstreet's cabal of enemies, including J.B. Gordon, Early and others, were very successful in (permanently, the author claims) assassinating Longstreet's character. Authors over the years, like D.S. Freeman, repeated the conclusions drawn by earlier sources and have thus perpetuated the lies.

The author's conclusion is that, in the final analysis, Longstreet's detractors had no stronger ally than JL himself.

Check out the Longstreet Society, if you haven't already, at www.longstreet.org.