1989 Suburban "V Rig" Gets Cummins Power

[v-man]

Ok, It's no secret, I'm no mechanic, although i can change my oil, and do lots of misc stuff mostly with my skirt on, like dusting, windows and carpet. But i need some idea's. After driving the V-Rig for awhile now and Vizsla's finally getting used to the Cummins, I'm only getting about 10-11mpg with intown/highway driving and occassionlly pulling my 12ft H&H dump 4000lbs empty. I'll admit the newness hasn't warn off and it's hard for me to keep me foot out of the carpet. ? is this about right or should I be getting better milage.I used to get about 13 with my 7.3 manual f-350 dually towing or not. I read in some of these forums that 17-20 is possible. Also what fluids could i expect to have draining from crankcase vent. Looks to be watery oil, possibly diesel fuel with a little black oil? Some farmers at the cafe said that may I might have a bad injector. Does that sound right? Thanks for any help