Currant is on my list of "really want it really really bad". But if I obey the laws of my state I can't have it b/c of the threat of it being a carrier of Pine Blister Rust. So, I can't speak with experience. But, lack of water, or too much heat may be the issue. I also think it is an acid...
I think you've got too much of a good thing in that hole! You might try pulling it out, inspecting the roots, and re-planting with your native soil, top dressed with a bit of compost. Check the pH requirements of the plant before deciding to loosen the soil with peat moss.