Maybe check the condition of the brake fluid,power steering fluid,and the coolant.Some replacing/refreshing there is a good idea.Look real good at the radiator/heater hoses for problems down the road.

Definitely do the plugs.Clean the mass air flow and throttle body and throw in a new o2 sensor if you feel froggy.

Definitely a drain and fill on the tranny.Flush=no good.

Would'nt touch the injectors with all the additive you run.too much IMO.