93 Suburban Misfire question...What Next?

[bennybbc]

I posted a while back looking for advice on which 91
or older Sub to buy. After lots of local searching I've
decided that I won't find exactly what I want. Well,
that and my wife has really pushed for the newer body
style of the 92 and newer versions. Ok, there are a lot
more of those available within a few hundred miles of
me anyway. What I want is a 3/4 ton with 4wd and
a 454. I found what appeared to be the best deal around
here in a 93. It has 130K miles on it but 34K miles ago
the original owner had a dealership put a new GM
replacement motor in it and had the transfer case rebuilt.
When I looked at it it was in pretty good condition inside
and out with a few exceptions. The shocks are worn--
about $350 installed for new shocks. The steering is
loose--Anywhere from $150 to $1000 with alignment
depending on if it's really simple or if it needs new everything.
The deal-breaker is that the engine has a misfire at idle.
Not really bad but bad enough that it wouldn't pass
California smog. The seller and I agreed that if he could
make it pass smog and get rid of the misfire I'd buy it for
$5300. That was almost $2000 cheaper than anything
else I found with 115K miles or more and none of the others
had the newer motor. The seller has had it in a shop for
a few days and the mechanic sounds like an idiot who's
just throwing parts at the problem. So far he's replaced
the EGR, the Prom chip, O2 sensors, Distributer, Plugs and
wires and both fuel injectors. It still has a misfire. Now
the mechanic says he's going to try replacing some/all of
the plug wires again. Huh? He's several hours away from
me so all of this is coming from the ignorant seller. I won't
buy it with the misfire. My next guess would be possibly
a burned valve but I'm no mechanic so that's just a guess.
I don't know if the mechanic has performed a leak-down
test. Obviously he should. The seller is just about at the
limit of what he will fix to sell this to me. Monday the new
wires go in but I'm not optimistic. The upper limit of what
I will spend, (on something this old) is $8000. I can't
imagine what else could cause this misfire at idle but I
doubt that if I had to pay for it myself it would exceed my
upper price limit. But I just don't want to buy something with
a mysterious engine problem.
Ok, so if this deal doesn't work out I'm done looking for
something with this many miles, new engine or not. I have
avoided the 96 to 99 Vortec engine because I've read a
few reviews that indicate that even though they're more
powerful, they also have quite a few more problems and
they're a few thousand dollars more, at least for anything
with under 100K miles. My next question is just how do
the Vortec Subs with a 454 compare in reliability to the
throttle body injected 92 to 95 Subs? I know they have
intake manifold coolant leak problems. What else? If I
spent $10K or $12K on a 96 to 99 with 60K to 90K miles
would I really be getting a much better Sub or would I
be spending a lot more for a nicer dash and lots more
headaches? I can't afford more than $12K right now and
even that is pretty much spending everything I got. There
wouldn't be anything left for possible repairs or upgrades.
Any advice from the list? Thanks for any help.
One last note, because of a severe knee injury that's not
going to be better for a long, long time, I'm very limited to
what I can repair myself. My best friend owns his own
shop and will give me a big break on parts and labor but
nothing is free...

Bruce
Redding, California