Did you weight your rig while fully loaded yet? you should get better MPG then that, unless your maxed out @ 8990. I have a 3500 ,maxed @ over 11000, and I get 17mpg(I have a lead foot also) A scan gauge will help you to monitor important info, other than PRMs much better. This forum is GREAT for info on conversions, but limited on running/repairing and knowledge of how a sprinter really works. Join the sprinter forum,
http://sprinter-source.com/forum/ and do some research there on the scan gauge and how to use it effectively. Pay close attention to posts by
http://sprinter-source.com/forum/member.php?u=2639 on the scan gauge ,you could even PM him(PM>>not a vistor message), Roger is a great guy and knows sprinters and how to set up and use the scan gauge very well