T.C.
I probably wouldn't back off on the potty training of a four year old. But I would back off and the pressure of it. Do NOT go back to pullups. Those things make potty training take SO much longer! Maybe just back off a whole lot on the pressure that he's feeling. Keep him in underwear, gently remind him, give him a TON of praise when he goes in the potty, and gently mention that it's yucky to go in his pants or something. With the poop, I would give him time to figure that out.
I guess my main point is to make sure to be very positive about it all. I know it has to be maddening! Back off on any pressure he might be feeling and just encourage him. Again, though, I personally wouldn't go back to pull ups. He's old enough that he needs to be in underwear. He sounds really stressed about it though.