Re: How reliable is the SOHC 4.0L V6?
I can only speak from my own experience, and to me, the 4.0 liter V6 has been ultra reliable.
Currently have over 450,000 km (about 270,000 miles or so) on the original engine and transmission (5 sp auto) with no major problems with either.
First two years of ownership, driving was about 75% to 25% city to highway - since then, it's been about 85 - 90% highway.
Most important thing, in my opinion, is to do the required maintenance, regularly - don't skimp/skip oil changes - done regularly on my truck every 5,000 km (about 3,000 miles), and transmission filter/fluid changes every 50,000 km or about 30,000 miles, like clockwork.
It will last if you look after it.
2003 Supercab Flareside
4 liter V6
4x4 FX4 Level I
5 speed Auto
4.10 LS Rear