newbe

hey everybody im new to this forum and duramaxs in general. I run a 95 6.5 but my brother recently bought a dmax. Its had some rough idleing issues and poor mileage but damn is it quick! We took it to dealer for the injector rate test and it passed also no fuel in oil. Dealer said to check inline screen. Anybody heard of that? I connected my snap-on scanner to it tonight and it has codes for cylinder #3 and #4 misfires. Does that mean the injectors are bad? Thanks