Elliott, I have a Denali cluster in mine. I got it off Ebay. I didn't have to have my speedo recaled because I only had 27k on my truck and the Denali cluster had 31k, so I just waited until I reached that mileage before I swapped. The only thing that is off is the hour meter. Yes you have to get it programed and the dealer can do it. There is a place in Martinsville Va. that can do it as well as Richmond Va. My trans temp gauge was plug and play.
If I could do it, which I can't, I'd have a dealer re-program the miles just so that it would be completely accurate.
I have heard that the trans temp guage is plug and play. However, like Jarrod said, you may need to have the dealer activate the temp output. I have only heard of that issue on the the 03+ trucks though, from what I hear all the 02 and earlier trucks are truly plug and play. Also, about mileage programming. Most dealerships will only program the mileage if its a brand new cluster with zero miles on it. Not sure if that's just a rule, or if they are actually physically unable to program it unless it is at zero miles. Every dealer I called said that their computer will not let them physically do it. However, I have a buddy who works at a chevy dealer back home. He claims that's bullshit.
I stuck an aftermarket cluster in mine, I loved the gauge faces. It had 97,xxx miles on it and the truck had like 130,xxx. I used an autometer trans temp gauge up in my overhead console. Having it in the cluster wasn't important to me. I didn't have the mileage reprogrammed because I really didn't care 99-02 temp gauges are plug and play You ever do it? Lets see some pics
FYI, the air bag light in the 1999 clusters functions differently than the 00-02 clusters. I'm not 100% sure, but I think it's only a difference in the software. If it is, you may be able to have someone reprogram an 00-02 cluster with 99 software.