There's a thread for folks looking for a GMT800 calibration for an L31 engine. One of our members uploaded a 5 speed L31 calibration to that thread.

http://www.gearhead-efi.com/Fuel-Inj...he-1-meg-PCM-s

Unfortunately there are no calibrations in that thread besides the manul trans calibration. If you'd like to add your VIN it may open a door in the future. I tried searching a few sites oriented toward used vehicle sales in Mexico but no luck so far.