Larmour Toujour

There are a few things you can do to improve the yield. 1. Leave the DNA to bind the membrane for longer. 2. Elute using buffer that has been pre-warmed to ~50oC. 3. Pass the eluate through the column twice. 4. Elute in the smallest volume (15 uL).

I believe the silica spin columns for gel extraction are optimised for a certain DNA fragment size range. I can't remember whether the gel extraction kit columns are better for small or large fragments, but your could try using miniprep spin columns instead because these will be optimised for larger fragments.