Your WAS (won at showdown %) is high, but you're not winning in the long run... The simplest guess would be that you're not keeping the pot small when you're drawing, and losing a lot of bloated pots when your villains take initiative on later streets.
2nd barrels (bluff on the turn) and 3rd barrels (a bluff on the river) as stone cold bluffs: These moves are to be played only against villains who have a 50% chance of folding to them or more. If you've tried it, seen others try it, and it's not ever getting the villain to fold, then take it out of your arsenal against this villain. They're calling stations.

When you're in position (which is always, right?) and you get donk bet into on the flop, think about why you might fold these spots. I'm not saying fold, I'm saying now, away from the game, think of why you might want to fold those spots. List some reasons: Your JJ don't look so good on AK3 rainbow, or your AcAs seemed so promising before you got 3 callers and the flop comes 876 all hearts.

After you make your list, go through your HH (hand history) and sort it down to WTS (went to showdown) and look for examples off your list that happened to you already. Think to yourself, "man, what a donk I've been! Look at that! If I'd just thought about this, there's no way I lose so much here."
Then look for counter-examples and think, "Crap! I thought I had figured this out, grrrrr!"

Let me know what comes after that part, 'cause I'm stuck on a loop..