Does anything have to be reset after installation of new ECM in a 1999 Isuzu rodeo?

Most of the time when a new computer is installed the new must be programmed with the information from the old computer or the information must be entered for the specs of the vehicle. Usually only a dealership can do this or a company that specializes in this sort of thing. The battery should have been disconnected during this replacement you should just connect the battery. It will take a bit of driving it for the new computer to adapt to the vehicle sensors and such. You might get some bad gas mileage at first few miles, but then it should get better. This has been my experience, anyway. Hope this helps. Good luck.