The engine sap itself isn't difficult and any 3.0 truck is new enough so that if you are
working with a same year donor the electrical part isnn't that bad...
But the additional complication of different motor mounts, different transmission bellhousing pattern, different exhaust Y-pipe, (and other mechanical differences)
make switching from a 3.0 to a 4.0 every bit as difficult as switching froma 2.3 to a 4.0.
The 2.9 guys have it easy by comparison, because the 2.9 and 4.0 while
different are closely related and the similarities outnumber the differences
I've said this before but it sems I need to say it again... "power" is NOT
what the 4.0 is about. going from 140hp(2.9) or 145hp(3.0) to 160hp (4.0)
is more than a trivial increase... but not by much.
On the other hand, going from 170ft/lb(2.9) or 160ft/lb(3.0) to a 4.0(225ft/lb)
is rather significant.
But what is most important is not the increase in total torque, but where
you get that torque.
The 4.0 makes more torque than a 2.9's 170/ft peak before it hits 1100rpm
(the 2.9 must spin to 2600rpm)
but comparing the torque of a 4.0 to a 2.9 while revealing to the benefit of a 4.0
doesn't approach telling the story of a 4.0 Vs 3.0 comparison.
the 3.0 has to spin to 3000rpm to make it's 160ft/lb torque peak
the 4.0 can do that at IDLE! and can continue doing it until it hits
it's rev limiter
Everyone talks "power", but what they want (without realizing it) is torque.
Yes, the 4.0 is probably what you really want, but swapping a 4.0 in
where a 3.0 has been is a much bigger job than most people are prepaired for.
I also voted for leave it alone.
AD