Actually, I was talkin to my mechanic the other day. We got on the subject of oil changes. I dunno if this applies to your 7.3, but my 6.0 has had a few "kick back" problems for about 6 months now. I changed the EGR, had the PCM updated and everything. Now, it only kicks back every 3k miles. After an oil change it drives like a brand new truck. Apparently theres a service bulletin out from Ford addressing this problem. I guess what's happening is the oil system is getting gunked up after about 100K miles or so. Ford's fix (believe it or not) is doing 3 oil changes in 3k miles. Do an oil change, run it hard, do another change, run it hard, then do the last change and it should be good for the usual 5-7K intervals between changes. Sorry about the long winded answer...but I'd say about every 5-6k is good.