Speedometer Cal for new tires 21 6.7L

Sorry if this is normal info, but my searches came up empty.

I'm a GM guy, but my friend has a 21 F350 Powerstroke he bought used out of state. He knows nothing about what has been done other than the obvoius...It's lifted. He sent me some pic's and I can see it has propane injection as well as a very much "not stock" looking engine bay. All he want's is the speedometer to read correctly. This is obviously modified, so not sure why the speedometer cal wasn't adjusted...unless it's something that can't be done. He's going to bring the truck by so I can look at it and see if I can read the file in the truck. I have no real knowledge of Ford tuning or diesel for that matter, so hopefully someone will have the answers to me questions. Thanks in advance.

-HPT shows the ECM needs to be unlocked. I am assuming this has been done already. However, if another "brand" tuner was used to unlock, will HPT read the write to the vehicle? If it does read, and the unlock was done with another brand, will there be issues if I try to edit the file and load it back in?

-Does HPT actually "read" the file in the computer for this platform? I know some of the GM stuff, the "read" file is actually a pre-loaded "stock" file to start from. Not knowing everything that has been done, and the truck is running great, I don't want to f*ck that up trying to adjust the speedometer.

-Are there any pitfalls when adjusting the Speedo? When I was searching, I found multiple posts (other vehicle lines) where the cruise would stop working or caused a CEL or some other stupid crap that I would like to avoid if I go ahead with this.

-Am I missing any other pertinant info that I should be aware of?

Reading ECM - You cannot read the file from the MD1CP006. You will only receive a "virtual" read of the ECM. Therefore, you must apply all tuning parameters to this new file to keep your previous performance adjustments.

Unlocking - If HPT indicates that the ECM needs to be unlocked, it has not been unlocked for OBD flashing. Most tuners are flashing directly to the ECM and not through the OBD.

Adjusting tire size - You cannot go above 34.5" tire size without causing things to get upset. Yes, there are ways to manipulate other data to adjust for this but it's not recommended.

slimmons2009,

Thank you very much for the information. This is pretty much everything I feared it would be. Since he doesn't even have a clue what's been done to this, I just gonna let this one be. An innacurate speedometer isn't the end of the world.

Thanks again