JD:
I had lower back pain once after peddling for an extended time too. I thought that it was my seat, and I have the new one. I added a 1 1/4" pad, made from an exercise mat, only on the bottom of the seat. It seamed to help the next time out, or at least I thought so. But the third time out I forgot the pad, and suffered no ill effects from the extended peddle time. I think in my case with all my war wounds, LOL

, it might have been old age.
A friend told me about adding the padding on the seat part, rather than on the back rest. He said that he thought his lower back pain was from his sciatica caused from sitting too long and peddling while on a wide seat - rather than one found on a bicycle - which put his hips more into play. He solved his problem with the pad. That's why I tried the padding in the first place.
HOPE this helps - worth a try anyway, and a lot cheaper than a new seat.