beating my head trying to figure this out please help

[WOLFMANmike]

ok so here is the Situation i have a 350 SBC in my 65 c10 i have replaced the cooling system with as fallows a new radiator aluminum champion 2 row for the bigger 1 inch cooling tubes .. i have replaced the water pump with a new HV water pump . i have a new electric 3000 cfm fan and a shroud . i have a new Tstat 180 deg and T stat housing i also drilled a few holes in the Tstat flange in case of Tstat failure .. i have also checked all freeze plugs and replaced with brass ones . the fan is on a auto switch set up so as soon as it hits 180 it kicks on . done a leak down test checking for bad head gaskets all is good. new fuel pump n new filters new carb a Holley 600 vacuum secondary . new plugs and new wires .. so now you know all i have done . here is my issue if its a warm day sitting in traffic or driving in town im just fine she sits at just 190 to 195 .. BUT the moment i start any kind of incline no matter how small she gets to the 210 mark not happy with that not when im running a 180 Tstat but here is where it gets really weird remember i have a fan shroud . so lets say im on the incline its a slight one but on the freeway and im not slowing down im doing 65 the whole time she gets to 210 but then as soon as im at the top of the incline and start going down still the same speed she starts dropping her temp back to 190 - 195 so please guys what am i missing here ? what is causing this and how can i fix it ? i mean if it was the fan not being enough it would over heat on any driving and if it was the radiator ? then i would think the same any driving would cause this .. and at speeds on the freeway as long as im forcing that air into it climbing or not i would think she would not over heat ? so yeah please help me figure this out