hey i was wondering if someone could give me some tips on how to get my fuel milage back up. I have a '90    w-350 cummins with a five speed. When i first bought the truck 2 1/2 years ago i was getting 18-22 mpg city/highway (and even back in march i was getting 19 on the highway driving over 75 mph), now i'm only getting about 16mpg all the time. and all of my driving is highway. And i have even been being real conservative while driving. From the best i can figure the truck has to have close to 275,000 miles on it but i'm not sure cause the odo broke at 221,411 almost 2 years ago. the rotary pump and the trans were rebuilt a few months before i bought the truck, but now the trans just started to make a howling noise when i shift down into 3rd or 2nd (it could do it in all the gears but there is too much road, engine, and exhaust noise after i get into 3rd) and reverse does it too. and i checked the oil as soon as i noticed the noise and it was full, as well as the transfer case and the rear. i have also been starting to use lucas fuel addative, but it doesn't seem to help or hurt my milage, although it seems like it gives me a little more power. I know that my truck is getting tired, but i really don't want to give it up. I would like to overhaul it, but i'm just out of school and starting work. so if anyone could give me some tips and tricks to get better milage til i can afford to breathe some new life into my old oil burner i would really appreciate it.