86'300ZX GL-L automatic overheating

[86300ZXVH45]

overheating first cropped up in mid summer (calif 85/90 degrees makes sense) can drive for miles on freeway , no problem. can drive for miles in town, no problem. try to combine the two in either order and gauge goes sky high) replaced water pump with a GMB 150-1280, thermostat with a stenson (?) superstat stn 45948, stenson (?) radiator cap stn 10227. I cannot see coolant flowing through the system with radiator cap off. But occasionally, faguely notice antifreeze smell in cabin with heater on.Please advise, thanks Bob