It sounds to me like you were getting exceptionally good mileage before your rebuild. I would love to get 25 MPG highway too! I get about 20 in my 2001. Are you 100% sure that your performance & mpg drop were right after your tranny rebuild? After all you said it was several years ago. Could it have been a gradual decline over time. If so it could be due to other factors. Have you tried any intake/exhaust mods? As far as the chip is concerned I'm not running one but have been considering it? My fear has been warranty issues & additional strain on my auto trans. If you are really unhappy I would try one. Just drive sensibly & use the extra power in a safe manner & reap the benefits of extra mpg. I know someone running a Superchips tuner on his powerstroke & he says it makes a big difference (especially throttle response off the line) & picked up 2-3 mpg. Just from sigs, it looks like most cummins guys are running Edge products. My .02 & hope someone else w/ more experience chimes in. LOL :gr_patrio