ISX 870 Jake brake is weak

[DKenworth]

[b][font=Times New Roman][size=large] Here is my story... jake brake became very weak. Overhead set was done like 150k miles ago. Was holding very good but lately i noticed that position 2 doesnt do anything and turbo boost is no more than 5 psi. Used to like working on and off. Last month local shop was fixing front of engine oil leak that i had for a quite long time, so they changed all guskets there. They had pulled all 4 gears out as you know. Everything is fine now, no leaks. So at that time i changed jake break wires and checked my solenoids, they seems ok. So, i dont know but it become very weak after they done front engine job. Should i done overhead set again or any thoughts? Where to look? Thanks guys. Engine is isx 870 with almost 1.1 mil miles, runs good. mpg is over - 7mpg. All cool except that jake break.