The 5.7 and the 5.3 are both Vortec engines from the late 90's. IIRC the 5.3 wouldn't show up in the Suburban until the 2000 body change but will be in the '99 pickups with the body change. If you're looking at a '99 or earlier it's probably a 5.7 (350)
These are among the best engines to have ever been built and can last to extremely high miles with a modicum of care. Ditto the intake manifold. They are some sort of plastic or resin and can warp to the point the gasket won't seal. Not a big problem to fix though. Transmissions were a problem but I think that was more in the mid-90's. Worth checking to see if one was rebuilt or replaced though. Obviously a lot of towing by PO might raise a flag. They will leak oil from the valve cover gaskets and eventually the oil pan. Not a gusher, just annoying.
If you can, jump to the newer body with the 5.3. A complete redesign that is every bit as dependable as the 5.7 without the oil leak issues. They made an o-ring seal on the pan and the heads are dished with flat valve covers so the v-c gaskets never have to hold "pooled" oil. The 5.3 is slightly less capable as a towing engine however so this might play into your thinking. I tow our 19' Sea Ray all over without problems though. The fuel economy on mine is about 16 for an average and can dip to 13.5 for all town and up to 19 for extended highway at moderate speeds.

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1983 M-B 240D-Gone too.
1976 M-B 300D-Departed.

"Good" is the worst enemy of "Great".