Prós
Work hard, and it'll be pretty difficult to lose your job. PACCAR take care of their employees. I had two supervisors during my nearly five years there, and both were excellent. They were mentors and guides more than supervisors. I know bad supervisors existed, but I believe this is the exception rather than the rule. They still have a pension, so far as I know (vested at five years). Seventy-four or whatever STRAIGHT consecutive years of profit can't be argued with. They have a good employee review process; I never had to ASK for a raise, they were already on top of it.
Contras
PACCAR are not afraid to cut the fat when they have to, but don't be the fat and GENERALLY you won't have a problem. If an old-fashioned conservative company (nice dress, no shenanigans, etc...) isn't for you, this probably isn't your company. There are definitely a fair amount of old and cranky people who have been there a few years too long and hate anything new and different. I can't speak to the new CEO, but Mark Piggott was pretty darn successful by most metrics.