I have a 2005 F-250 6.0 164k on it and a couple months back had the BG service plan done on it, well when I go at a high rate of speed 65-70 mph for a long period of time the wrench light comes on. I just got it out of the mechanic to look everything over before I left from Oklahoma to Colorado said everything was fine and look ok to him he hooked it up to diagnostics nothing came back, this is my first powerstroke to own..it does have a Bully Dog gauge tuner on it so I'm wondering if the air filter could be setting it off since it's a little dirty, I do have weight on it! I am pulling a trailer fluids are fine it's pulling great but I am confused on why it only come on when I'm going fast for a long period of time and it's driving me crazy. Someone help!!

 

Just a suggestion, try removing the "tuner" and see if the problem is still present. Mind blowing problems many times are caused by add on fixtures that defy explanation.

 

If it threw a wrench light you should have a stored code. Not all scan tools pull all of the Ford codes.

Also, you need gauges that read engine parameters. Most likely you could have had an overboost or your oil cooler could be getting plugged up. Lots of good phone apps out these days. All you need is an ELM adapter. Monitoring MAP, EBP, oil Temp, and coolant temp are the place to start (after trying somewhere else to get the codes read).

My first guesses would be over-boost or oil temperature, but you can waste a lot of money on guesses!

 

What level of tune were you pulling at?

Like bismic stated,, Free apps/downloads like FORSCAN and an inexpensive ELM327 adapter USB cabled to a Windows based laptop gives you a fairly potent diagnostic tool for under 20.00 (depending on who's adapter you purchase) and help not only retrieving codes, but Live data parameter/values that may point to the issue.