sounds like ignition problem. most likely coilpacks died. easy to troubleshoot. unplug one each time and start the car - you will see which one works or doesnt. if you have consult cable - read the code. should show 21 if ignition. also ignition module can die if all coilpacks dont act consistent. spark plugs just unscrew and read. rb motors like ls coils swap. read on gtrcanada how its done - never worry about sputter or hesitation again. oh and get rid of 255. rb dont like walbro. good luck
edit: my phone bad