C15 low power

Hey everybody, Well I hit a deer in my Kenworth and it totaled my truck, so I decided to go buy a newer one so that I would not miss any work. Well I settled on a 2003 peterbilt with c15 475, supposedly turned up to 550 and 13 spd. Well I went to haul my 1st load with it and it seemed to be really low on power. I had an overhead done on it because it has a new head and I thought they may have messed up. They said the valves were way out of adjustment and I figured that was the low power issue. Well tonight I hauled another load and it still seems to be struggling. I had a new fuel pressure gauge installed as the old one was disconnected at the motor so I hooked the line up and it is showing about 100 psi at 1500 rpm. The guage flutters really bad though, it flutters between 5-10 psi with the motor rhythm. Boost is about 28 with the wastegate pinched off. Shop pressure tested everything and fixed some small leaks. Injector cut out test passed. Egt is 650 max pulling hills. New air filters as well as fuel. I'm stumped. I'm trying to not sink a bunch of money in this right now as I spent a lot of money getting a new PTO and blower for it. Any ideas? I've read numerous threads and I've done most of the stuff everyone recommended. Are these normal readings and maybe I'm just not use to this new truck. The only thing I can think of is there is a pinging noise from the passenger side i think top end, everyone I run with said "it's a cat, its gonna have some pings and ticks" but I'm not so sure. I appreciate any help given, thanks

 

It is the 6nz

 

The head was installed before I purchased it, I ran it for one night shift and thought to be low on power. I changed fuel filters and found a bunch of rubber crap in the water separator. Thought that would fix it, still low power. Took it to the shop, they did injector cutout test, pressure tested the air to air, found some small leaks so put new clamps on. The did an overhead and told me they were way out of adjustment, I was hoping that's what caused low power but it did not seem to help much, maybe marginal improvement. They installed the fuel pressure guage and it shows 70-75 at idle but like I said, it flutters 5-10 psi with motor rpm. Truck doesn't seem to be missing or hesitate any, no white smoke, gets a little puff of black down low but that's normal

 

They said they tested for leaks and found some small ones. I usually do the work myself bit I run night shift so i just have them work on it during the day. Guess i probably ought to do the pressure tests myself

 

That's a lot of leaks lol, I'll try and buy some PVC fitting to do it myself tomorrow, I would like to say I trust their word when they say they did it but I'm not sure