You really need to weigh out how bad you want that 5.3 though...These forums make it sound like you can just drop one in (not saying these guys above but just in general) Back before I replaced my 350 I looked verrrry heavily @ doing this and got everything lined up. This isn't just you buy a 5.3 and put it in. You'll need a whole new computer, custom wiring harness, motor mounts, custom flex plate, engine, and not just any shop can do it. This takes someone real special. It takes a lot of research/work/effort to do. Also if your tranny also has that much mileage on it, then you can go ahead and plan on rebuilding that too regardless of what "new" motor you put in. 350 or 327 will break it, so be planned for that as well. These 4l60e's aint all that. With these truck you've got to plan for what could possibly go wrong because chances are it will.
My original engine was burning oil BAD, so I said oh I just need an engine. Bought the crate (used but looked PERFECT internally) wasted alot of $ getting it in and running. It had an awful rod knock a couple months later and the stock trans lost reverse. Ended up buying another motor (this ones good) and had the tranny rebuilt at the same time. Sorry for the long ramble but I'm a firm believer you should go ahead and rebuild that tranny or replace it along with the motor. A unit that old with 180,000 miles becomes one. Tranny gets used to that motor real well then all the sudden there's a new one with fresh power and then you're back @ square one.
Like I said sorry for the ramble but I promise reading this may save you a HUGE headache. Yes for sure go with the 5.3 but only if you're prepared and willing to do alot of research and hard work, oh and $...These type swaps seem simple but it adds up VERY quick. To be honest though if you want to go with a crate motor, put a cam, heads, intake, and full exhaust on a new 350 and I think you'd be very happy. The cam and heads on these TBI's are a joke.
