I thought I would post my experience in the hopes that someone else doesn't have to travel down the same path. A little background first. I recently purchased an 85 blazer with a bad engine. To put my mechanical ability in perspective I installed the new engine in a day and a half and had it runs great. This is about the 5th engine I have installed or helped install. My dad helps me with most of this and his mechanical ability is way above mine. So I assumed that with some extensive research and a little time it would be no sweat to install new gears. The 3.08s and 35 combo just wasn't ideal to say the least so a switch to 4.56 was the natural thing to do. I spent nearly 3 weeks researching on how to install the gears. Printed numerous post and instruction sheets as well as watched a video that came with my gears 3 times. So I feel that my preperation was more than enough. By the way the full size chevy website has a great writeup on how to install the gears. Now to the mistakes. 1. Take everyones advice and have someone install them for you. Yea I know saving several hundred dollars is a lot but chances are you will "dealing" with issues in your rear-end for several weeks if not months if not years. I would love to see the stats on the people that installed gears and got it right the first time vs people in my situation. I think this would be very lop sided. I have completely had mine apart twice and had the chunk in and out at least 15 times during the first install. So my point is let the trained mechanic be the one to deal with all of this. I now have to pay to have my stock gears re-installed and am either going to sell the truck or wait until I have the money to have someone install the gears, which by the way the front cost more than the rear (quotes from 100 to 200 more). This is after spending at least 36 hours of my time on it. 2. If you still have to do it yourself, Buy ALL the right tools the first time. This was probably my downfall. I thought I could get away without some of the spec. tools. Trust me you can't. But in my opinion that still isn't enough because you need to have a good feel for what it should be like. And that can only come from experience in my opinion. 3. Make sure you have a adequate set-up to do the work. I have seen advice given that you need a truck load of patience to do this. Well from experience if your workspace is inadequate then you need 3 times that much. I had a nice shop to work in. But with no car lift there is only so high a truck can be. Even with 9 inchs of lift it gets real old being hunched over under the truck for several hours trying to get tolerances within thousandths as needed. It also needs to be very clean. Any dirt, trash, etc... will make the job much harder and add to the frustration. 4. There are two things that I greatly underestimated. The first is that reading a pattern on low gears is very difficult. I spent hours trying to get this right and basicly had to settle. The second is that setting pinion preload is VERY VERY hard and VERY VERY VERY important. Figureing out when you have crushed the crush sleeve and the getting the right inch pound preload is extremely difficult. For the first timer, all the directions I recieved are vaigue at best in describeing how to do this. This is something I think can only be done right the first time if you have had experience. Again just pay someone. I know that some people will not agree with me and that is ok. They were able to do it right and saved a ton of money. Which can happen but you need to one have a lot (more than you could dream of) patience and get a little lucky. So if you are thinking about re-gearing maybe this will at the least make you think about it a little more before you dive right in. And you won't spend a ton of extra money. At least a feel better now that I have vented. One last thing. I think the best adive I have seen is if you want to regear find some 3/4 or 1 ton axles that have better gears and swap them. Would have been much much better and cheaper in the long run.