I think it depends on what the mods are. I believe things like CAI, exhaust and headers etc would do very little to harm your truck and some would argue they would actually prolong the life of your engine (and I'm in that crowd). Engines are basically big ovens, the more air in and out, the more they breath, the less heat. Suspension work would also be safe in my books.
Bolt on mods I reckon are safe. You can ALWAYS improve on a factory design, always (that's how cars evolve) so what's factory, isn't always safe/right. It might have been right 9 years ago (2004 trucks etc) but that may not be the case now. Factories know guys will mod their cars, it's accounted for and is business. Leave it open for aftermarket sales = more $$$$.
There really is no way to tell other than getting two trucks with 150,000miles, one with mods, one stock and compare them in terms of exterior stress and drive-ability. Even then it'd be hard. Remember, every single engine is different so no truck is equal. A SC truck may out last a stock engine, in this game, it can simply come down to good/bad luck.
I also agree with Yellow Venom, it also depends on how you drive it. I have and always will drive my toys the same, hard. Not a "dumb f#%k" kinda hard (like careless, etc) but I always get stuck into the gas pedal when I have a chance to do so safely, burnouts, get loose, etc. In short, I love being a hoon!!
IMO, when you drive a car and use it as intended (Ie: SRT - Sport Racing Technology) they just seem to get used to it and perform well forever. When you baby them, it's like you're wrapping them in cotton wool and when you do unleash it, it's like they're not used to it and it hits them harder than normal? Hard to describe but yeah, drive and use them as designed, have fun and most importantly, service them regularly and they'll last and last. 2c
