Hypertec has hand held devices aor they give you a chip to put in. A chevy dealer would not do it. Did you but the truck used? If you did maybe your husband is having them put back to stock. If people use the hand device and don't return the stock program you would need to reburn the chip to factory specs.
To be honest I don't know how the TST works. I believe it is like OL said and it adds to the system in place. If you want it back to stock you just remove the box.
I had the superchips hand computer for my gasser I had. I could program the motor and trans. It does not even come close to what a desiel box will do.