Plastic tanked merc. radiators do not often plug up...this is from the local radiator shop owners mouth.

Since he just did all this work on the cooling system most likely its still air causing problems.

I thought my rad was bad before too...talked to the guys at the shop...turns out my fan never full engages when it is supposed to. Another dead viscous clutched fan.

BTW I'd be lookin at the fan and other such things before I started dropping cash on the radiator...they are NOT cheap.