GM - are not too bad with their stuff - they are clueless about small 4 cyl engines but e.g. the old buick small 6 which is this engine
General Motors 60? V6 engine - Wikipedia, the free encyclopedia
was designed in the 70s and still is a very good engine, it works for ages - its problem was the lower intake manifold gaskets leaking coolant into the oil (its an old style american engine which was originally meant to be carby hence old coolant passages in manifold). You can see them with twice as many miles as any japanese engine. (I have one chevy impala with this engine).
btw - the problem with GM is their management - they are nuts - they put a gasket in the manifold that gets eaten by their dexcool coolant - they never put out a remedy themselves but aftermarket companies have provided it.
other american engines - like lets say the Ford 4.6 modular V8 in the crown victoria is like a rock - it serves taxis everyday day and night and police cars and all other government agencies too.
Both the above engines are very robust but are not anything near high performance - they are infact quite lazy low rpm slugger engines which have gobs of torque low down in the rpm range.