Plants can wilt from too much water, also from too little.

Where is the soaker hose placed? At this time, water needs to go directly into the rootball.

Perhaps change to building a berm at the edge of the root ball, another at the edge of the planting hole. The inner basin (rootball) needs water far more often than does the outer.

I have the soaker hose circled around the base the tree a couple of times. It is not touching the trunk, and only goes out about as far as the branches do. Is a soaker hose an effective way to water a tree?

A soaker hose is possibly the best way to water a tree, provided you run it long enough so that the water penetrates deep enough to provide moisture to the entire depth of the rootball. And to test properly for adequate soil moisture, you also need to know how deep that "still very damp" soil actually is.....a couple of inches is not deep enough :-)

It's virtually impossible to tell you from this perspective whether your situation is the result of too little or too much water and/or poor drainage. Or maybe something else altogether, like the newly planted tree just becoming acclimatized. It happens. All you can do is to make sure your tree is getting enough water but yet not too much. Japanese maples absolutely require good drainage. If you amended a planting hole of heavy or clay soil with rich soil amendments, you may have created a sort of inground bucket, with the enriched planting hole capturing and retaining water and the clay preventing or at the very least, slowing good drainage. For heavy, clay soils a very shallow but quite wide planting hole is recommended, with the top of the rootball placed slightly above grade. Backfill only with the soil removed (loosened as necessary) up to the top of the rootball, creating a small mound or berm. The alternative is to amend the entire planting area, not just the individual hole, and ideally to the extent of the projected mature root spread. But the recommendation is to never amend the planting hole - what comes out goes back in, nothing more. Any amendments perceived to be necessary should be applied as a mulch or topdressing.

Gardengal48, thank you for all of the info. This is my first time planting a tree, and even though I thought I had done a lot of research before hand, I guess it's live and learn!
I think I will get a moisture meter to help me decide when to water, and hope that the tree pulls through. It hasn't lost any leaves yet, which I guess is a good sign.

I think the full sun is the problem. I have much better luck with coral bark in some shade.

I have 2 Coral Barks that do rather well in part shade and another in full sun. The full sun maple does not do as well as the part shade coral barks.

I am thinking oliver75 may live in the PNW - our spring was one of the worst in memory, being extremely wet and far cooler than normal. Here virtually any Japanese maple can be grown in full sun as we are far enough north that even midsummer sun is pretty mild compared to anywhere else in the country. Coral barks in full sun are extremely commonplace and is actually a recommended siting for this area. You can get some discoloration or premature color change on foliage from stressed maples for a variety of reasons, including too much/too little water, poor drainage, poor soil quality, transplant shock or too radical a change in siting. But since most growers of JM's grow them full sun as well, the last is not all that likely.

Oliver, it would be a big help with any future postings you might make if you would identify your location to include your hardiness zone and general area. You can amend your member page to do so. That makes it a lot easier for responders to address their responses to your specific situation/location.

I bought a moisture meter, and sadly, have found that my soil is not draining. I think this was because I dug the hole too deep, thinking that it would be helpful with drainage. The hole was probably as deep as it was wide. I also amended the hole thinking it was the correct thing to do, later learning I probably shouldn't have done that. I do think I created a 'bucket effect' like gardengal48 commented on.
At this point, I know it is only a matter of time before the tree starts to decline. Could some one please tell me what I should do? I really would like to keep it in this spot if at all possible.