I run a Diablo sport tuner, and have their performance tune in my car. I have not dynoed my car to know for sure, but always feel that after a few months it seems to lose power. After reflashing it, it seems to have more pep and better throttle response. When I watch the live data it shows an 8% long term fuel trim, is that about right and have any of you guys experienced similar problems?

Wish I could help, but I run SCT.

I would check out www.modularfords.com and speak with Chris Johnson who actively posts in the Diablo section.

The tune is the same. Reflashing the same tune shouldn't make any difference.
You should get a custom tune...assuming that one is a mail order deal.