I can almost guarantee it will need 3-4 clutches replaced. I would get a factory unit repair manual (it is a factory service manual for repairing transmissions and transfer cases) for the year of your truck if possible, if not as close to as you can. They are usually on ebay for a decent price and it will have exact procedures for rebuilding your 4L60E. I rebuild a lot of 4l60E's and they are not hard and will function perfect if you follow the unit repair manual. A used transmission is a huge gamble and may not last long if it does work depending on its history. If you choose to have someone else do the work make sure they aren't band aiding transmissions selling it as a rebuild, I have seen too much of that in my area. The best of luck to you fixing your problem, wish I could be of more help.