XT program came out in the late 90's and was only put on Macks that were all Mack (I am sure there have been some excetpions) 2000 and up Macks should have the 460P rating avable 487hp from 1500-1900rpms a straight 460 and 460E torque cuve is as flat as Kansas the P rating put alot of Arch in the curve ECM would be step one Step 2 North West deseil makes high flow injectors now for E7 and E-tech 30-40% increase so it is possible to up rate the motor to around 550 you would need watch the gagues running one that hot I have 01 Vision set for 427 and a 13spd and have plenty of power