What Sevvy said; it is hard to say that it's not effective just like it is, without reading a sample of it, if you want to post some in SYW. But just the fact that you say you haven't learned a damn thing about him in 40K words tells me that your instincts might be right; you might have a cardboard guy running around doing stuff.
Try this: Think about what
internal conflicts this guy might have. They don't have to have anything directly to do with what he is doing, but they will need to feed into what actions he takes. However, you can work it backwards from what you have already written, you don't have to change your plot. Take the actions you already have him doing, and come up with an internal conflict that would be plausible to make him do those actions. (PS edit: if you work it backwards this way you may need to change some plot actions to make it consistent, and you have to guard against "tacking" it on to force it to fit.)
For example, he's hiking in the woods and, coming around a curve in the trail, he confronts an adult bear up on it's hind legs, roaring at him. What does he do and how can you weave internal conflict behind his action?
* He turns and runs
Internal conflict - he ran from bullies back when he was a child. He is conflicted because he feels he can't stand and fight like a man. You can place a memory or two of bullying incidents in dialogue or you can show this in a minor incident early in the book; he buys something at the store and is shortchanged by the clerk but the clerk disagrees and he backs away and leaves feeling cheated, and worse, weak and inadequate as a man. Now with the bear, instead of writing, "He turns and runs. The bear chases. He grabs a nearby tree branch and hauls himself up... " and so on, you can write, "He turns and runs, like the coward he is, and the bear chases him. This time he's going to die for being such a sissy. He grabs a nearby tree branch and hauls himself up...." and so on. Now you're seeing inside his head, not just his external actions. And it is the
internal conflict that allows you to show what is inside his head.
* He pulls out a .44 Magnum and shoots the bear
Internal conflict - he reacts instantly and with violence to most confrontation, even minor.
He was the bully in school. He has had trouble keeping control of himself all his life. For once, today, that flaw has paid off in a good way. There are appropriate times to react with swift violence. But, standing over the bear carcass, and now seeing the motherless baby bear off to the side of the trail, even though he knows he probably just saved his own life, he feels, once again, that he has been a "bad boy".
* He drops to the ground and plays dead
Internal conflict - he learned as a child that the best way to minimize the beatings he received from his drunken father was to pretend to have been knocked unconscious with the first blow. Likewise, he figures playing dead will make the bear lose interest. But as he grew up, the trick worked less and less with his father, and he suspects it won't work now, indeed, the bear swipes his back with it's claw, ripping his shirt and gashing his flesh.
* He yells at the bear, opens his arms and spreads them wide, making himself look as big as possible. Then he picks up a rock and throws it hard at the bear.
Internal conflict - When he fights with his girlfriend, he yells too much, and puffs himself up with self-righteousness, once in a while grabbing a knick-knack and throwing it on the floor to emphasize a point. This has caused a big problem in their relationship because he broke the prized Hummel that was her mother's, who died last year. The internal conflict is that he knows he needs to handle arguments in a more mature way, but hasn't quite learned how yet. His way of handling confrontation may, or may not, work with the bear. Read on to find out....
So, no matter what your character does about the bear, you can deepen his character and reveal what is inside his head by planting these stories earlier and then just making brief references to them during the action.
In previewing this I read your post about him in the woods and blaming his psychosis on his wife's death, so you already have plenty of fodder for internal conflict. You just have to pick the action, or non-action, that he's doing, and use phrases here and there to relate it to an internal conflict you've given him. It doesn't have to be complicated but it should be clear to you. For example:
The reader knows where mitch is, as we follow him through the mountains of tennessee. He does get a little lost and doesn't know what state he's in, but the reader won't know either. And we get an idea for where he is when he slips on the loose gravel on the side of the mountain, or hides behind the chopped down stumps in the obliterated forest. I just realize that while I'm showing you the flowers and destruction as he passes it by, you have no idea how he FEELS about anything.
Suppose the biggest internal conflict he has now is that since his wife died, he feels life is not worth living anymore. How can you inject that into his walk in the mountains so that we see inside his head? Just add some simple statements:
"He slips on some loose gravel. Great, why not just slide all the way down the mountain, splat on the bottom and get it all over with."
Shows how he feels. You don't say, "he felt like life was no longer worth living". You just make what in this case is a sarcastic jab about slipping on the gravel. You don't have to get too flowery or lengthy about it. In fact, it is probably better if you don't. During action, characters (and readers) are thinking more about the action anyway. But you can deepen character and get into close third inside his head by simply adding small phrases here and there, such as "like the coward he is" when my guy ran from the bear in the example above, as long as those phrases reveal a consistent internal conflict going on... your job is to figure out what that conflict is (conflicts are) and to weave it (them) through the whole story. By the end your character can resolve the conflict, or not, whatever is appropriate for your story.