isx torque guage questions

[TB3NNI5]

Long question, hope i explain well and am looking for some knowledge on the subject. To give some background info, 2014 cm2350 factory 485 18 spd with 3.08 rears, when i first got the truck it had already been turned to 500hp per the computer where it shows advertised hp. It was very weak, wasnt holding rail psi, i diagnosed bad injectors and replaced all 6 from peterbilt. Had decent power after and torque guage always went to 100% in a pull and just seemed to pull better. The only problem i had was the truck was always chattery like it had no pilot injection, it eventually through the months seemed to lose power and eventually i could only squeeze 85% torque out of it, i know these are generally vague readings but why would it use to push 100 and now only 85? What causes this? I have since had the truck retuned and got rid of all that chattering and noise it use to make and hazy idle it had. Ive had to do an inframe along the way for dropped liners, intercooler etc. truck is very healthy overall no engine lights etc, if one ever comes up im quick to adress it. Im just very ocd and feel like its not trying as hard as it should. Advertised hp says 601/2250 now, but pulls no better than it did at 500/1850 tuner guy says it should be a good running truck but its just not... Also, does anyone know if i can turn off the “brake lights coming on with jake brake” function with cummins insight?