well general rule of thumb is:

for a gas motor, over 200k miles is pretty old. 150k is getting up there.

for a diesel motor, the motor isn't broken in until at least 100k, and typically 250k is when one would say damn that truck has alot of miles on it.

 

Haha, ya i did too until i bought my truck. All i can say is if you keep up on your maintenance like it sounds like you do, your engine will last a heck of a long time. I have driven 4.0's with less than half the mileage of mine that feel weaker and closer to death than mine...it all comes down to how you treat em.

 

^ I sure hope my truck lasts a heck of a long time! I need it for a good 4 more years at least lol. But yeah it really does come down to how well you treat the truck. My dad had an 2000 Expedition with 5.4 Triton (Beast) that was maintained down to the book and he finally traded it in 2008 for a 08 F-150 (5.4 Triton 4x4). The Expedition had 225K on it and still ran great. However the tranny fell out of it around 160k but I reckon that's pretty good.