I have a 2003 Chevy Express 1500 Cargo without cruise control. Is it possible to add this, and how would I go about doing so?
You have two options: aftermarket cruise, factory cruise
Most car alarm/stereo installation shops will be able to get and install aftermarket cruise control.
You can order them online such as here
General Motors Usually only has one wiring harness for the vehicle, meaning the vehicle with all the options has the same wiring harness as a vehicle with none of the options. Now there may be a sub harness (short leg that plugs into the main harness) that's not there but the base wiring is there.
Check with your local dealer, you should only have to by the switch, control box, and throttle bracket (may be there already). Plug it in, add the fuse and you have factory cruise.
An alternative to the dealer is to get the missing components from a vehicle equipped with cruise at a salvage yard.