The Ford Motorcraft fuel additive is good stuff. One bottle treats 125 gal of fuel. Make sure to use the one for 6.0 PSD as they make one for the 7.3 and it's different. If you have never used it before, put a whole bottle in (1 quart) when you fuel up and get on the highway and drive it like you stole it. That additive will keep the EGR from coking up and sticking. Sells for about $6.50 a bottle, that's cheaper than any mechanic.