We had a '97 F-350 with the 7.3 PSD many years ago. Not the greatest high-end torque but loved it! We now have a '14 F-350 6.7 PSD. Love it EVEN MORE!
I wouldn't worry about the 6.7. 157K miles is just now getting broken in
Best engine Ford has put in their F series trucks. As Rugbyref said; just have it checked by a qualified mechanic.
Pulling power is AWESOME! We have a 16,000 lb 5er and it doesn't even know it is back there. The 6.0 PSD does have some power/pulling issues and the 6.4 PSD has some fuel economy issues... hence Ford developing the 6.7 without their past association with Navistar.