Check out this thread:
https://www.ford-trucks.com/forums/1...it-affect.html
The problem code, P1249 is Wastegate Control Valve Performance issues.
It could be that your 20 year old turbo wastegate is sticking, needs cleaning, etc or it could be a PCM issue with the Map Sensor not sending the proper signal or with the PCM not responding to the inputs.
If there's no appreciable change in engine performance, no "fuel delivery compensation" from the PCM, I'd suspect it's not a critical failure, rather something that's dirty, carboned up, sticking or "just old"....
A good diesel shop can probably pinpoint the exact issue and tell you whether it needs repair or if you can ignore it/chip the truck to change the parameters or whether you need to fix/get it fixed.....