No sure why they would flush and replace the radiator?  Do you have a leak
in the radiator, that would be the only reason I could think of that would
warrant a replacement.  At 130k if you had regular services done, you don't
think you should have to rebuild or replace the engine.  I had more then
that on my Ram when I traded it in with no problems.  You could run a little
ATF through the oil and that would break down and get rid of some of your
"sludge" which may/should help restore some oil pressure.

A switch to synthetic after 130K of Pennzoil might have loosened
accumulated crud. I once had a Toyota that suffered recurring oil
pressure and ticking problems, beginning a couple weeks after I made the
brilliant choice to treat the truck to some swell Mobil 1 synthetic oil.

There's a recent "oil viscosity" discussion that will show you the
general quality of azwiley1's advice.

Change the oil to 20W50.

beekeep

IF there is sludge in the engine. then yes you can drop the pan, replace
the oil pump and pickup screen, clean the pan out and put it back. but if
you take this route you have to remember that there IS sludge thought the
rest of the engine and IF it gets disturbed it breaks loose and comes down
into the pan.

here's your issue (assuming there is sludge and i don't doubt it) sludge
breaks free from farther up in your engine, washes down with your oil back
into the oil pan where it floats around waiting to get sucked up by the
oil pickup tube. now this tube is only so large and has a screen on it to
keep stuff floating around in the pan, like sludge, from getting into the
oil pump and stopping the whole works. now over time sludge will build up
enough in the pan that when the pickup tube gets totally covered your oil
pressure drops to zero, as you have seen, this of course means lack of
lube.  when you shut the truck off, the sludge floats away, thus the
ability to start it back up with oil pressure (in case you were wondering
about that one).

in my experience, its best to replace a severely sludged engine because of
all the stuff that can break loose and put you back in the same boat all
over again.  if its not that sludged up, or you just cant afford to
replace the engine yet, then replacing the pump, screen and cleaning the
pan will buy you some time. the amount of time depends on how severe the
sludge condition is inside your particular engine.

also I'm not personally sold on engine flushes. I'm a bit of a skeptic
when it comes to "miracle in a bottle" type stuff. that being said I've
never disassembled a engine that has been "flushed" to see if it actually
helped. so this is simply my skepticism talking.

as far as replacing the radiator, I'd have to know more of the story. like
why does he want to replace the radiator? does it have scale in it? is it
stopped up? or is he just wanting to replace a good radiator while doing a
engine swap as a precaution of some sort? again I've always used the old
radiators on my swaps AS LONG as they passed the pressure tests and sown
no leaks or clues to being stopped up before hand.

Thanks for the info...We actually got info today that there are some
metal shavings in the oil pan. The mechanic also noticed a bearing was
loose. Although the engine never stopped on us, we are being told to
replace it completely and that just changing out th pump and other
will result in the same problem again soon.

Since the engine never ceased in us, is there anyway to just clean all
of the sludge out and replace the pump and other and put a better oil
and be OK. Or, do you pretty much just have to replace an engine once
it has too much sludge? Even if it is still runs? Seems like that is
what everyone has to do with this situation. It's a pretty big bill
for an older truck and we do use it for hauling heavy things but if we
are gonna spend any money, I want to make sure I don't overspend if it
is not necessary but I don't want to crack the engine if I start
pulling a trailer behind it. Thanks again for the help!