Can you make a complaint that a police investigation is taking too long?

Making complaints is your right.

But the police when annoyed can do some really good vehicle/traffic enforcement when their abilities are questioned

The Health Department and Social Services can get involved too.

Ask your local News Services (TV/Newspaper) if they know what is going on.

No, not successfully anyway. In most jurisdictions, police services are stretched very thin. Compound that with an ever increasing workload and pressure to get things right the first time, it can take quite some time for an investigation to be completed.

Anyone can complaint about anything and in your case the complaint should be addressed to the District Attorney's office.

Yeah but dont do it its a long process and it stresses people out big time

This is America. You are within your rights to complain about whatever you want.

Sure. Will that do any good? No They have no obligation to go faster for you.