Can anyone explain this... Dyno report??!!!

It says that you only have 78 percent of your rated HP. You lost boost in the higher RPM range which could indicate a boost leak or lack of fuel. I didn't see the truck pull so I can't comment on the cause but I would follow the mechanics recommendations of fuel filters and cac boots as he did the test.

 

The report should go to 1200 RPM and when I did dyno runs we always figured the hp at 82%, Fuel preasure should be a standard measurement, to me it is a waste of time without it. We use to do exhaust back preasure, intake restriction, boost and fuel preasure, fuel restriction, fuel temp, if ran for over 15 minutes
Get the CAC tested at the turbo, to the engine, any boots that leak remove the clamp and loosen the boot from the pipe, and soap down the clamp and tighten it that way the clamp will tighten around the whole thing not just 50%. Air out the breather hose is from valve guides and a couple of cylinders, Check the boost guage as well as the boost sensor, with a manual guage in the system. Then test the CAC alone.
Just a thought!

 

My last carrier had Peterbilt 379's long hoods with cats mostly. All trucks from 94 to 97 purchased new. Trucks #19 and #20 were 94's with 435hp 1550lbft 2100rpm 10 spd eaton with 3.70's, these trucks got the poorest at around 6.5. #21 and #23 were 95's with 455hp 1650lbft 2100rpm #21 had 13spd and 3.55's #23 had 15spd and 3.55's these trucks consistanly did 7.25. #24 96 model and #27 was a 97 model both had 475hp 1650lbft 2100rpm 10 speed eatons #24 had 3.55's and #27 had 3.70's. #24 got 6.75 to 7 and #27 got 7 to 8.25...yes 8.25 that was my last quarterly ifta in that truck. # 28 was 475hp 1750lbft 2100rpm 18spd with 3.55's it got around 7. I was around these trucks from 98 on. I drove all of these trucks and most I put 50 to 200k in each one. I was kept on til the end in 2012. Trucks #19, #20, #24 had been to cat and probably got low nox files put in killing their mileage. Truck #32 had a detroit and consistantly got the same or better mileage as #27 til it had an overhaul at Williams Detroit Diesel. It lost 1 mpg after the overhaul as they advised us they put a newer emission file in it at overhaul.
I would leave it alone if it still has the factory file in it, but if you took it to a Cat dealer I bet they put a low nox file in it already. If you are going to uprate I liked the 455's the best. They made they 475's look stupid climbing jellico at 70 to 80,000 with stepdecks.