99 Tahoe running sporadically

We have a 99 Tahoe with 94000 miles have been having problems, it will run for about 100 miles and then start sputtering like it is running out of gas and the anti lock brake light comes on. RPM's drop, gauges go to zero. Will act like it is out of gas, will shut down but will restart. Have replaced crank positioning sensor, put in new computer, new battery. Fuel filter has been checked. Believe previous owner hit something on driver's side, has after market front bumper, head lights, fender and hood. Before new computer the codes were un recognizable. Does anybody have ideas what we can do next. Have only had vehicle two monthes.