First of all I need to apologise for asking a Ford question on an IH website, but the technical minds and talent in this community are far superior to what I can find on any Ford website. (I fully understand if the forum moderator wants to dump this post!) I figure there's plenty of people here with the Navistar engines, so this is not totally non-IH related. Having shifting problems in my wife's 99 F-350 SD 7.3 6-spd CC Dually. About 99k on the odometer. Bought the truck at 30k assuming original clutch, and have not touched the clutch since. Almost 100% tow miles with 2 to 5 horse trailers or 20k equipment flatbed (it works hard) Started having problems getting it into gear about 20k miles ago, like the synchros were not allowing it into gear. Drained original fluid and switched to royal purple synthetic hoping to free things up. The problem is intermittent - when shifting it slides into neutral fine, but won't go into the next (or any) gear at times. You're left stuck in neutral which can be vary scary when you're on a packed interstate towing horses. When it's operating normally, there is a fair amount of resistance when shifting - like you apply pressure and need to wait 2-3 seconds before it will slide into gear. My guess is a problem with the synchronizers. I understand what they do, but not completely clear on how they do it. Seems about the same in all gears, so I expect it's a fluid issue and not one bad syncho (I'm assuming each gear has it's own syncho gear) Based on use and mileage, I would not be suprised if a worn clutch has some impact (no slipping yet, no other reason to suspect clutch was bad) Any ideas?? I'll post this one the FTE site as well - I expect the typical response to be something completely useless and dumb like "switch to an auto"