A question for the experts,

I have an 89 Auto Carat in New York City, lately the weather has been cool,
yet yesterday around 70 though. I have noticed that in the stop and go
traffic that the engine temp gauge can get almost to the top. I have 20/50
oil in which kept it cool during the summer but lately I have noticed that
gauge creeping upward somewhat quickly.

Do I need a radiator flush?

New radiator?

Different Coolant? (It has the phosphate free stuff in it now)

New Heads? (The van has 150,000 Miles on in and still runs very strong)

Or I am just paranoid and this is the norm?

Thanks to all in advance.

Robert
NYC