CAT 3406E

Hi all,
Rolling around a 1999 379, 3406 1LW, 13spd.
Been slowly but expensively getting it repaired and trying to get it 100%. It's turned up to 550. But when I load it out and start rolling, seems like I'm rated 300. I've replaced the ECM as it apparently was fried. Put a new tps. Tested the air to air. New fuel filters, air filters, fresh oil change.
When I'm bobtail, I'm driving a Porsche, empty trailer she feels like I'm pulling 20k. Load out to 78-80k and you can hang it up getting to speed, pulling hills, over pass, etc. Getting maybe 3.5-4 mpg. Anyone got some ideas what I could check, test, or replace? I'm not too worried about what is going to cost to get her 100% but it'll break me not running 100%.
Thanks stay safe

 

Thanks, I should have added it's be checked with the computer, that's how we found the ecm was bad. It was saying it had under 4200 hours on the ecm, but all the saved codes we're 45,000 plus recorder hours. Interesting enough, the tps wasn't sending a code. When we hooked the computer to it running, press down the throttle, it would have like a dead spot, but not at the same spot. Since replacing the tps, it stopped stuttering, cutting out, when I would turn left. I've been looking at the different post on here and other forums, seems like a common problem with the E models, but I haven't found a fix yet.

 

A guy that works at CAT in ABQ, we just don't have to pay the shop prices. I'm not sure about pressures, if anyone has a link for some gauges, I could definitely look into getting some numbers for it. The trans pump on the front of the block was replaced in January as well. I'll ask if they did calibrate the crank sensor. I've heard that atmospheric temp sensor could cause low power problems, but I have been unsuccessful at locating info to test it with a multimeter. Any knowledge on that would be appreciated.
Also I've read and the first reply here says to have a dyno done. Anyone got some locations to get that done. Google returns shops in places we don't go. NM, CO, TX, AZ is our primary area we run.

 

For sure. I'll check around see what I can find for doing a Dyno on it. It would be helpful to know how much is getting to those wheels.