We have a 2002 Yukon XL with a little over 200,000 miles that’s been sitting idle on the driveway for over three years. The body is in good shape and the interior is in fair shape, however the transmission needs to either be rebuilt or replaced. Because of this lengthy idle time, I’m sure it’s going to need some money put into it to get it back into running condition again. I’m trying to decide whether it’s even worth the money for that plus the transmission. Let me know if anyone has any suggestions or advice.
Get a couple of estimates for a tranny rebuild and compare it to the value of a running vehicle…It’s probably a coin toss…A salvage yard used tranny is a possibility but these are always a crap-shoot. You might be better off just scrapping the vehicle instead of pouring a lot of money into it with the results a gamble…
List: transmission 2000.00 - tires 800.00 - oil change and fluids 200.00 or more and no real feeling of how much more it will need. I say bail now.
A 13 year old vehicle with 200,000 miles that has not run for 3 years and needs a transmission! Unless you have a lot of time and money, send it to the crusher.
You will end up spending more than it’s market value to make it fully roadworthy and safe.
You could drain as much of the old gas out as possible, add a few gallons of fresh gas along with an additive such as SeaFoam or B-12, stick a new or borrowed battery in it, and see if it’s going to run. Some rough running is to be expected at first but should (knock on wood) clear out.
If it runs fine then a decision on the transmission could be made at that time. If it’s looking very problematic on the engine running then you would only be out the expense of some gas, additive, and possibly a new battery if one had to be purchased.
If the battery in your current vehicle is 4 or 5 years old the new battery may not even be a loss. The new battery could possibly be substituted for your old one and prevent the new battery being listed on the debit side of the ledger.
When it comes to cars I’m generally of the glass half full type until something tips it over… 
@ok4450 is absolutely right. You have essentially nothing to lose trying to start it. I will only add that you should make certain there is oil in the engine, coolant in the radiator and a fire extinguisher somewhere nearby. It might surprise you and start and run OK.
Thanks for all the good feedback and advice.