The most "severe" service it might see currently is on the parkway between my house and my dad's house. That's 9 miles of 60-65mph cruising. My math puts that in the 3000-3250 RPM range and it's most certainly not heavily loaded.
I don't know how many miles it had on it when he had it rebuilt... Well I know the odometer reading but since the engine is not original to the truck and likely neither is the odometer... not to mention I have no idea how many miles were on the donor car. I'm betting it was well over 30,000.
I know straight 6's are tough, I have a '95 F-150 with the 300-6 and it's pushing 200,000 miles with nothing but oil changes.
