… diesel, battery, hybrid gas and electric systems, and hydrogen fuel cells. While GM researchers had made progress by 1998, the technical hurdles were steep; and GM believed it … diesel, battery, hybrid gas and electric systems, and hydrogen fuel cells. While GM researchers had made progress by 1998, the technical hurdles were steep; and GM believed it … diesel, battery, hybrid gas and electric systems, and hydrogen fuel cells. While GM researchers had made progress by 1998, the technical hurdles were steep; and GM believed it …