I have the same problem with my 280ZX. No problem on open road, but stop, go and the needle starts climbing. I have two electric push fans and a solid engine driven suction fan, shrouded sealed around the radiator, tried different thermostats, tried different electric fans, played with the timing curve (Pro-Flo EFI) and nothig works. No air pocket problems as filling point is the highest. (See pic's in member gallery)
I am in the process of getting a custom copper radiator made up as the allunimum one does not seem to do the work (Cost of $750 - thats how fed up I am with this problem) . Will have it fitted by this weekend and give feedback.