99 lumina-Tune Up?

Just bought a 99 Lumina with 36000 on it. The previous owner was a smoker and car is dirty with 3 small burn marks. I got it for 4000.
Had a mechanic look it over and he said the car was very good.
The antifreeze looks dirty so i bought a flush kit and with prestone flush it out. Then change the oil and pvc. Now is there anything else i should be doing to tune it up @ 36000 miles and get it in tip top shape.

Check the Air Filter and Spark Plugs. Other than that I think you re set. For the long run keep an eye on the coolant level especially if it's the 3.1L and I hope you don't experience the infamous intake manifold leak or headgasket failure.

Thanks, I changed the oil & filter and air filter too.
The coolant didnt look to clean so i flushed it with prestone super flush. The guy told me it would take 12 quarts of dex cool. When i filled it it only took 1 gallon of coolant and 1 quart of water.Does this seem right.
I hope so. I was told the mix should be 50/50.

Yes, the specifications for the amount of coolant are strange. My haynes manual also says about 12 quarts whereas in reality only about a little more than gallon fit in mine. I get the feeling the cabs or police luminas have that much coolant, they have the heavy duty radiator which you could actually buy. I think it's twice as thick.
The mixture should be 50/50 and only use distilled water!