Is it too late for my evaporator coil in my central air conditioning unit? I get no suction after cleaning...?

From your description of the coil being "pretty dirty" and even though it's been "cleaned" in place, I'd have to say that coil is plugged with dirt. As Phillip said, the coil will have to be removed from the air handler in order to clean it thoroughly. Those slab coils aren't easy to remove and they aren't easy to reinstall. There are a couple of tabs on the back of the coil that protrude through the cabinet and they are a pain in the to align. The coil might look clean on the surface, but the dirt gets embedded further into the coil. If the coil is that dirty, I'd imagine the blower is pretty dirty, too. I'd remove the blower and clean the blower wheel if I was going through all the trouble to remove the coil. Are you sure there are no restrictions through the return air filter grill and that the platform opening is cut out the same size as the bottom of the air handler?