These GM engines are solid engines, the intake man gasket being the weaipoint. Take what you buy and closely watch the coolant tank and the oil. If anything suspicious appears, change that gasket immediately. All these are 200,000 mile engines (that's what I call them anyway). And here is a key piece of information, if you change the gasket use new bolts and not the old bolts with the 3.1 and 3.4 as they have aluminum heads. Many mechanics won't do this because they don't keep up to date with the TSBs on the engines. Personally, I'd even use new bolts on all three engines. Bolts stretch when they are torqued and to get proper set you must use new bolts. The 3.8 was awarded one of the 10 best engines of the past century by Wards publication, I can't tell you how many of these I've seen with 200K+ miles and still running strong.