You can’t install an after market cruise to a 6.5 TD. The 6.5 TD is drive by wire and has no throttle cable to install the aftermarket cruise control to.
If it does not have cruise, then you have to do a couple things to get it.
First is to find a used turn signal unit from a van (1997 to 2000) that has cruise or buy one from the dealer. Replace the original one with the new unit (you have to remove the steering wheel)and you should be able to use your new cruise. You can buy a new one from the dealer, which is 300 plus dollars or you can get it from GMPARTS.com or something like that. Remember the Gas part is the same part you need, so look in a junk yard (recycler). Oh yea, you don’t need the cruise module that the dealer will try to sell you. Everything is in the ECM under the dash.
AND
If after you install the new turn signal unit the cruise does not work, than you have to either go to the dealer or a company that does tuning to have the cruise option turned on in the ECM. Most of the Savannas with Diesels are fleet ordered, which means they did not come with cruise and the ECM was programmed with a fleet profile.
An alternative for cheap people is to add two switches to the dash, an on/off and a accelerate/decelerate switch. There are only four wires that are used for the cruise control.
Any questions, pm me with it with your email address so i can reply.