Ok another update
Hi Guys, long time no see...i have an update.
I started to measure better my fuel consumption (Odometer in zero/fill the tank/drive some miles/fill up again/register miles traveled/drive more miles/fill up again/etc) and here are some conclusions.
August 1.- Went to fuel station.Filled up the tank. I deliberately drove until nearly empty. It took 78 liters to fill it. Odometer in zero.
August 15.- Went again to the same fuel station,same fuel pump,same hour.Filled the tank again.It took 56 liters to fill it again.Odometer at 182 miles. So i think with minor calculations that the truck got aproximately 12.28 miles to the galon (please correct me if im wrong!) 90% are city miles (but not stop and go traffic,really more like expressway)i barely used the a/c
August 22.-Went again to the same fuel station,same pump,same girl,at night(different hour).Filled the tank.It took 71 liters to fill it.Odometer at 460 miles(278 miles traveled).Again, i think i got 14.80 miles to the galon.50/50 city/highway driving with lots of 4k/5k shifts and max/ac.
According to certain websites,with my tires(31*10.5*15 vs 235/75/15) i´m driving 2% more than the odometer readings, so the figures should be a little higher.
Well, i think the truck is running at least ,good.The bad gas mileage is at least normal.Note that the last improvement i did was the rear brakes,so "maybe" it was a factor which affected my mpg. I still want to change my rear differential fluid so i´m waiting for the parts (yeah,down here is HAAARD to get a damn rear differential gasket!)
Anyway,thanks for all the responses.Please feel free to correct my calculations and give me your comments.
Thanks !!