First of all, PEH says nothing tongue in cheek.

With regard to the mileage, you don't necessarily need to be worried about the mileage, but, as a general rule, engines, transmissions, and rear axles wear based upon mileage and a vehicle with 221,000 miles has more wear than one with 150,000 miles. Clearly this is obvious to you. Can one of these engines go 400,000 miles. Of course, but, they will definitely be down on compression by that time and you will definitely notice the need for some attention. Can the transmission go 400,000 miles? I suppose so, but, this is very unlikely. 200K is considered typical for these units.

You just need to be mindful of the mileage, not be worried about it.