2000 Chevy Blazer bucking and jerking a lot

2000 Chevy Blazer mileage 59,000: My Blazer has been bucking and jerking a lot lately. It's a 5 speed. Bucks and jerks as you gain rpms in each gear. It usually starts at around 1800-2200 rpms, but varies. I have had the service engine light come on a few times and then it goes out after a while. I’ve tried new plugs, wires, distributor cap and rotor. I took it to the Chevrolet garage and they said it was a fuel pressure regulator leaking and replaced it at $382 and it is still bucking and jerking. They then said it had plugged injectors they were cleaned twice and still jerking. They said the codes said cylinders 1, 3, 6 were misfiring. They said bad gas they dropped the tank and cleaned but then they said it wasn't the gas after all as the tank was clean. They replaced the fuel pump after breaking the sending unit on it and replaced the fuel filter. It is still bucking and jerking the service engine light came on again. They said codes say cylinders 1, 3, 4, 6 are misfiring now it needs injectors in all 4 cylinders. Would this be correct as it sometimes seems to run GREAT and other times it bucks and jerks. I'm at a loss as the Chevrolet garage “seems” to be guessing now and it is getting costly for a “no fix” so far $643 for the 4 injectors replaced if it needs it as they say it does. Any suggestions?