are you using the silencer when you fire at them?
if not its your aim...
at the part where you have to disable the GPS station I leaned out behind some cover from about 50 yards away from the humvee that pulls up with the guy firing the machine gun at you and I took him out with like two three round burts while he was shooting at me. That was without the silencer attached on Delta.
I just think you guys suck at this game