We did not have any issues with the 8.0. It ran good and did not have any tuning issues. Still got decent fuel economy. I just went to 7 to make it a little smoother band, which it did seem to help. I also done it for better run time. I really do not know if it helped the run time because I did not try a before and after. The 6.5 just did not seem to run as good in the ones that tried it and tuning was a little off.