If your subs not seeing much excursion it's not seeing much power. I'd put $50 if you turn your gain up you'll find your missing output and excursion, along with turning your box around. DD-1's are a waste of money, this is literally the 3rd thread in like a month where someone who "tuned" with a dd-1 says they have no excursion/output but are right on the verge of clipping. If your clipping a thousand watt amp for a 15 in around 3 cubes and aren't seeing any real excursion either your sub has a few extra spiders on it by mistake (JOKE) or you NOT clipping a 1000 watt amp. a -10 tone is VERY quiet, while this normally makes for a "loud" gain setting, your gains are barely turned up. If your gains are barely turned up on a -10db tone and with gains almost bottomed it's close to clipping, then you'd be clipping with gains at minimum on a 0 and probably even a -3 tone. As others mentioned you'd be clipping the **** out of it on real music, and again, you have no output, doesn't seem realistic.
1. Go play a bass heavy track and slowly turn up the gain, ignore any clipping lights, if your tuned mid 30's try a mid 40hz track, airforces is an easy one.
2. Turn up the gains until you see the sub STOP moving further. You'll see a small change at low gain, at some point things will really begin to move, when that stops happening, back off.
3. When you find your peak excursion take the gain down a tad.
If you do that, your not going to be clipping very heavily, usually that gets you pretty close to a 4:1 gain overlap. Yes, it will clip on heavy stuff, but it's mechanically safe and unless your woofer really can't handle your amp, the minor clipping wont' hurt anything. After that try a few other songs, low stuff, high stuff and see how it is.
I know this sounds very simple, but if it' simple.. Why not try? It's alot easier than finding a new box builder that everyone says is the problem despite never seeing the inside.