Anything I should look out for on a 4th gen 88 GMC Truck?

More of a Ford guy but was offered one for a decent deal. I have experience with the SBC and 700r4 but nothing otherwise.

Anything I should look out for?

Depending on where you are located rust could be an issue. I had a 2500 diesel of that generation and based on my experience I'd look at the following:

- fuel tank and tank straps, especially where they hook into the frame cross members. 
- The rear spring hangers to be sure they are not getting weak from rust. 
- Check all the lights for any weird behavior that could indicate ground issues. 
- oil cooler lines (if it has one), they can dump all the oil really fast if they let go. 
 

Other than the rust/ground issues and normal maintenance it was reliable. It ended up using 3 engines and 2 transmissions to reach more than 700,000 miles when I sold it. 

They are pretty robust. Nothing is expensive or hard to fix. If it's not rusty you're good to go. Pics?

Be aware that they are remarkably slow.  The engine and trans tend to last a long time... which makes sense because they're only 180hp (early) or 185hp (late) and 300 lb-ft.  Or worse, 170/250 for the 305

If the plan is to add hp, just fair warning... they are not a good platform for it.  Every single aspect of the engine is very well suited to the low output they make; dished pistons, worst-flowing heads ever on any SBC, tiny cams, TBIs don't flow much and the ECMs are not capable of compensating for nearly any mods.   If the plan is to just drive it as-is, great choice.  Check the block casting (bellhousing flange kind of under the distributor).  Not many - but some - of the early TBI engines were cast as a roller block even though they got flat tappet cams.  If more oomph is in your future, at least it's a block that has that going for it.  You can at least keep the block, crank, and rods, but most everything else will need to change.

Watch for little puffs of blue (oil) smoke at startup.  It's not a big deal, but GM used cheap valve seals on the TBI engines.  A little puddle forms on the valves which makes the puff.  Not a real issue, but it can dramatically shorten catalyst life and I did notice on mine that a few of the plugs got fouled a little faster than normal.

MPGs will likely be much less than you anticipate for the low output.  With 3.73s my 1988 K2500 could barely muster 13mpg with a tailwind, and towing 6000 lbs took it to 7-8 mpg.

Also look for rust by peeling back the weatherstripping at the top of the windshield.  They sometimes let dirt and water get in there and one day you'll suddenly have a very wet interior without warning.  As a hot rodder, I really dislike the TBI for many reasons, but if you're just looking for a truck to do truck things and don't mind going slow, they're a great truck.

Thank you very much everyone for the info.

I just want to do truck things with it so extra power is meh. It did have headers on it and didn't seem to be as gutless as I feared but it has 20psi at cold idle of oil pressure and it took a bit to get to that level. It also got to a whole 25psi at max at highway speeds. That's less than I'd like to see.

No smoke or blowby though and the transmission is strong. No real rust issues but an unsightly dent and a black spray canned hood. Front end is at "scary vibration" because the upper control arm bushings are years beyond gone.

And as funny as it is, I also apparently got a concrete job from him lol

That "25psi max oil pressure" doesn't sound great.  Not sure how much fun it is to swap main & rod bearings with the engine in the truck.  I would be most worried about the trans and rust and it sounds like those are currently okay.  Unlike Curtis the '88 we had, a 2wd/305/700-R4 truck ate a couple of transmissions in the 200,000 miles we owned it. 

Ours was pretty trouble free otherwise. Garbage factory paint which is a classic GM issue of the era, body rust in the common spots (rear wheel arches, one of the cab corners), etc etc.  Nothing really exotic or even interesting.  Oh, and the stupid baby sized radio making swaps a goofy affair. 

The oil pressure sender has been replaced in mine multiple times. I'd suggest swapping in an ACDelco sending unit first. 
 

400k miles, still tows. 
2018, first Miata.

2019, second Miata. 
 

2021, challenge car.

Last February I towed about 800-1000 miles over a four day weekend. These things are durable. 

The oil pressure sender and gauge was new. I obviously can't be sure it was working perfectly but it didn't do anything I would consider symptoms of a failing sender. It would raise a little with rpm, it wasnt reading abnormally or doing anything strange, just reading low. It took a good 10 count for it to raise off zero when I started it. None of these are particularly good signs.

If the body was better? Sure. If I didn't have to rebuild the front end right away? Sure. If it was cheaper( although it is pretty cheap)? Sure, I'd investigate to see if the sender was failing but.....I'm not in a hurry and it's not exactly what I want. 

What viscosity oil is in the engine, and how many miles since it was changed?

Floating Doc (Forum Supporter) said:

What viscosity oil is in the engine, and how many miles since it was changed?

No exact idea on either.

Brake line going to the rear is attached to the inside of the left frame rail. The fuel tank is very close to the left frame rail and dirt/moisture/salt build up will cause the line to rust and fail. Difficult to do a visual inspection.