I have a 2009 Pro Star with a cummins isx. I picked up around .6 mpg when i first installed it 4 years ago. I was doing a lite weight dedicated run that allowed me to run 54 mph. But since then I started doing loads that required me to run 65+. My Fleet Air Filter failed me about 6 months ago. I have been using paper filters and my 90 day avg has dropped to 6.52mpg. The good news is the awesome people at Fleet Air replaced my filter for free!! It arrived today so I will install it before I get back on the road March 9th.
I went thru LM in Las Vegas, NV. If you do go with LM, just make sure you get the truck checked out real good. And be sure to get it dyno'd and do a rig dig. If you dont, and have a break down and try to get warranty work, you may not get it. Plus if you get it inspected and find things wrong, they will make the repairs. But once you sign and drive it off the lot, it's your problem. The people at LM Vegas are real nice. I got a 2009 Prostar from them Dec 2013. The whole transaction took 2 days. Including taking it for inspection and dyno. The price of the truck was in line with the International dealships. $4200 down and $1395 a month for 42 months.