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Old 08-11-2017, 08:44 AM   #10
jmcarter
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Join Date: Dec 2008
Location: Richmond Hill GA (and Port Ludlow WA)
Posts: 2,410
Default Re: low fuel mileage

Based on my experience with two 5.9 Cummins (both with manuals) 10.5 MPG seems reasonable, particularly towing 70. Have you tried towing at about 1500-1600 RPM? You're likely to get 2-3 MPG improvement and then you can do a cost analysis to see if a gear change is reasonable.

BTW your indicator is probably optimistic by at least a couple of MPG. Also, unless you plan on burning up another stock auto best leave the tuner stuff unhooked.
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