What exactly are you wanting? To just change the first page wallpaper or to change all the pages of wallpaper?
To just change the home page of touchflo3d you slide your tabs over to "settings" and then click "wallpaper" chose a file and you're good. This changes just the home page.
If you want every page changed you can do one of three things.. set up for panorama, set up for nUmbackground4all or over write your sprint manila wallpaper file.
Advantage of panorama: as you scroll through the tabs the image pans across the screen, kinda cool
Disadvantage: You must use an editor to change backgrounds however you can create several set ups so you can swap them out.
Advantage of nUm setup: Can change wall paper the same as changing the home page, slide over to settings and choose a file.
Disadvantage: Can not have separate home page wallpaper, must use flip clock
Advantage of custom file edit: Changes every tab to same wallpaper, do not need to switch to flip clock, can have separate home page wallpaper
Disadvantage: Can not switch every page on the fly, must create several sets with the editor.
Now that chainfire's editor is available it is so easy to do the bottom choice (overwrite your sprint wallpaper manila file) because you can connect your phone via active sync usb, access the file from the cfcgui editor directly, import new image and immediately overwrite to the phone or save to your desktop for later use.
Chainfire's editor is here:
http://forum.xda-developers.com/showthread.php?t=470798
Use the latest version!
File to overwrite is: