No, you are right. 30-40k is ok, if it hasn't been a hard 40k. If you have a guy that goes and puts 150hp into his truck and pulls his back hoe around before wanting to upgrade transmission you are playing with fire.
I should have been more clear. 99% of the time if the truck has less that 30k you are fine, even with the aggressive ones.
After 30-40k, I need to know a lot more about the truck and its use ans service history before I can confidently say, "You will be fine after this upgrade." I just don't want anyone to be misinformed about a product or service they may purchase from me or any of the other sponsors. We are here for the members.