Is the turbo lag worse that the normal 1.48 sec? (Stock ECU set turbo lag)
Anything changed?
Things that can cause smaller diesel issues, and lower power-(more noticeable on small engines but bigger trucks see it too)
Dirty filters, (Fuel, Air, oil Etc)
Water in your fuel (increases stuff growing in the fuel)
Stale or lower grade fuel, (biocide, as several bacterial eat the stuff in the fuel, algae growth in tank, etc, PowerService, or other Cetane booster can help too)
Things I learned-
Buy premium Diesel where you can, worth the 10-20c more a gallon,
Buy diesel at stations with a higher turnover (near highways, less likely to get stale or bunk fuel)
Do not buy if truck is filling tank or for 6 hours after (if you can avoid it, it stirs up all the silt and stuff in the tank that needs to resettle)