Talking with my uncle today about Ford trucks. He mentioned an additive that is supposed to be added to the antifreeze every 5000 mi. Must have missed this somewhere. I have put 15,000 mi without the additive on my '01 7.3L F-350 since buying used at 34,000 mi. Is it critical?

yeah, that filter thing sucks hey? i have to do that 2 times a month with the miles i put on. otherwises sorry, no additive for the antifreeze but i am having great results with diesel FUEL anti gel additive! howes antigel, not only keeps the fuel from geling but cleans and lubes the injectors and IMPROVES my gas mileage to the point that it more than pays for itself on the mileage improvement! you can get it at any truck stop and i use it year round for a couple of tanks at every 5 k miles as well as every tank below 15 degrees.