I have a completely stock 2000 gmc with a 01 c.o.s. and i average about 14.5 m.p.g. I am looking for anything to help me for a few extra m.p.g. I have turned off cat protection, and tried bumping the timming 15% at cruising speed, but not much luck with any of these. Any suggestions????

the truck as 120,000 miles and is tuned up as well.