The U3D file format has some odd issues that allow only a map of 1024 x 1024 to be applied to any one mesh.
We had a test version of Enfold 3D that supported higher resolution U3D file output but it caused the polygon mesh to be broken into separate pieces. We made the decision that it would be better to have the connected and complete mesh output and deal with the lower res texture map on the back end.
Here's how you do that:
Open the U3D file in Strata Design 3D 6 or 7 (yes, you'll need v6 or higher for the U3D file format support).
Locate the texture for your Enfold model file and open it. Click on the thumbnail for the Diffuse Color map to open the Image Map dialog. From the View Scale pop-up menu select 100% (the view scale effects the resolution that the map gets copied at onto the clipboard).
Now copy that image. Go to Photoshop and create a new document. Paste the color map into the new document (you'll notice that the image is squished and has a black boarder on one side. This is compensated for in the UV mapping of the mesh).
Now go to the Image menu and select Image Size. Increase the resolution of the image to a size you feel will support the renderings you intend to create. You now have a high resolution, blurry texture map. Now we fix it.
Open your original package design in Illustrator. Hide everything except the art you want applied to the box and choose "All" from the "Select" menu and copy. Now go back to Photoshop and paste the art into the Ps document your created earlier. If you want to be able to edit the art and retain the ability to size it up to even higher resolution choose "Smart Object" from the dialog asking you how you want to paste it in.
When you paste the art in you are automatically put into Transform mode for the art. Now scale the art to match the fuzzy placeholder art underneath. Now add black and cover where need be to make the new art look like the old art. Now you can do Select All and a Copy Merged to paste this higher res map back into your Enfold project in Design 3D - or you can save the Photoshop document and use it for a source to link to the surface of your Enfold model via the texture linking feature in Design 3D.
It's a little complicated - but we've used this technique many times and don't find it to be too difficult. In the future we hope to resolve this in a more automated way.