well I have used and known many folks that have used there trucks as a tractor, from pulling 8 ft gang disc, to spreading lime with a ground driven lime spreader( 2 ton at a time)
I have also seen trucks used for many other things
the issue's I have seen are pretty simple
U joints failures, being at the top of the list, it seems pulling things for long periods of time that have constant resistance(like a disc harrow like wise)
add a ton of stress to the drive train, that a truck just isn;t made for, not to mention the added stress on the differential gears!
also a truck is not really designed to go that SLOW working things as hard as they get worked when pulling things with a constant drag/load!
so you end up with some added cooling issue's and concerns
that and add in pending what truck your using, your using a pretty costly vehicle to do the work of a much cheaper tractor, PENDING TRACTOR of course!, tractors can cost way more than a pick up truck
I once was at one property that was set for a work day, and 3 of our tractors went down for stupid reasons,
and we ended up using a older 3/4 ton gas dodge pick up truck to disc a 3 acre plot, then pulled a rented bulk lime spreader to put down 6 ton of lime, and then re disc'd the plot 2 more times!
the truck worked, to be honest was kinda comfortable too boot, out of the fresh air and dust from all the lime, and running AC a radio ,
but by the end of the day, the truck was about boiling over, and both front axle joints were clicking and ended up being replaced, and not too long afterwards the re drive shaft U joints went
I know all were not NEW, but the added stress and all that LIME dust, that stuck to grease, and then that non stop load on things, sure shortened there life span!
HAD it been a daily driver truck one drove up to property, they would not have been driving it home AS IS<
and again, I have seen this happen several times over the past 30+ yr, when a truck gets used at a tractor!, so it wasn't a once time issue that popped up!
this is why they make tractors, and when you compare a rear end on a tractor to a pick up truck, you see a BIG difference really fast!
and don;t forget trucks have piss poor turning radius , which in it self can add to issues , pending where being used!