Here's an endgame I had a little while back against a strong player.  I came out of the middlegame up a pawn, but I wasn't able to convert it to a win, though I felt like I had some chances.  Any good endgame players have any suggestions or feedback about where I went wrong?  I'd appreciate it!

20.Rxd7 ? why not Qc3. 40. why not Ra2 look after your a-pawn ? Could you not hang on to your queen for a bit longer before you exchange it.

43....e5  44.Rxg6 again to help your a-pawn

Tough one.

Maybe 38. b4 was one inaccuracy? Start with the furthest pawn and push it first with38. a4! and I think it gives White +/- and good winning chances.

38. a4 and now Black has many options, but Rxe4 is really not one of them as it leads to an immediate winning K&P endgame for white after 38. ...Rxe4 39 rxe4 Kxe4 40 b4 ! So....Black needs to find some waiting type of move and on any one White inproves King position with Kb5 next, threatening to gobble up the loose a-pawn.

This is one way I might try it at that stage in the Rook endgame.

That is a very good suggestion, richie_and_oprah, I hadn't really considered 38.a4.  It does look like it gives White some good winning chances.