I owned an '89 and a '92 - both with 4.3 and loaded with options including
A/C

Both went well over 200,000 miles.

As a matter of fact the '92 is STILL running for another owner.

Maintenance was no more difficult than most other vehicles.

I did my own routine maintenance.

I would suggest a "routine maintenance" fuel pump change at 100K. Both my
vans needed one at around 125K-130K - as did my current GMC S-15 pickup
with the 4.3.

It is just "normal" GM maintenance.

Both vans did around 20-21 mpg and "lost" one mpg to A/C - which I figured
cost me around 25-cents per hour travelling down the highway in the late
'90s.

My current pickup will do up to 23 mpg on summer fuel, with a similar
one-mpg loss for A/C, but even if it was twice the '90s cost - 50
cents-per-hour - I feel the A/C/ is well worth it....a couple of bucks to
be comfortable during a four-hour trip.