Well I had read a thread about being able to grease our front wheel bearings via the vacum line port. Since I have manuel hubs I had a black rubber plug on it. My front stub shafts seem to go too often. I was on the roads and had to do something. I took my Amsoil 2000 filled grease gun and put about 60 pumps into each port just holding it tight. Well I deliver new travel trailers. I've gone from 16.5-18 mpg empty to 20-22.45 EVERY single tank empty. It also feels free rolling where it would drag down apon backing out of throttle. I have put about 12,000 miles on it over the last two weeks and it is consistane. Towing is up about 1/2-1mpg same trailer. my truck has 420,200 miles now.