Weak Endgame/Failure to convert advantages

I am roughly a 950 rated player right now. My tactics trainer rating right now is 1400. I find that in almost all of my games I always acquire some sort of material advantage pretty easily in the openings and middle-game, usually a couple of pawns or a minor piece or maybe more. However, once we get to the end of the middle-game and into the endgame, I find I begin to deteriorate in my play. I often end up in a considerable positional weakness, and sometimes I even lose despite my matierial advantage.

This has happened for the past dozen or so games (both on chess.com and real). It is so frustrating to see what seems like a relatively won position degenerate into a loss, and I frankly don't see why.

Can anybody help me here? How can I improve my endgame and help convert advantages into wins?

I have bought Silmans Endgame Course (I am to read only the first couple of chapters, according to my higher rated friend) and his other book, Amateurs Mind. Will reading these books lead to me acquiring a significant improvement in my endgame?

For your level, tactics are far more important than most endgames except for the very basics.  I'd recommend reading Jesus de la Villa's 100 Endgames You Must Know as a crash course in the most important things in the endgame that covers a lot of key points.  I don't like Silman's endgame course as it's a bit simplistic and only covers broad points while claiming to offer something valuable.  That's the difference between Silman's endgame course and de la Villa's 100 endgames - they both offer similar things, but de la Villa's doesn't pretend to be anything more than a crash course for players who don't want to put serious study into the endgame while Silman's claims to be a comprehensive manual when it really isn't.  Fundamental Chess Endings by Muller is good as well for the basics.  Another excellent book is Van Perlo's Endgame Tactics, which emphasizes almost all of the most common tactical tricks and finesses used in the endgame.