93 grand prix issues

I have a 1993 Pontiac Grand Prix LE 3.1 it stumbles and cuts out while driving and sometimes won't start. When it won't start there is a clicking sound under the hood while the key is on. We've replaced the fuel pump, coil packs, coolant temperature sensor, egr valve, intake air control and intake gasket, fuel relay. I really don't want to buy any more parts I don't need. Please help!!!

I also wanted to add that we got code 54 when we ran a scan. And it sometimes lunges forward when it starts. We are thinking we should try replacing the computer. Any input would be greatly appreciated.