1991 Chevy Caprice over heating and install

we performed overhaul on my caprice,we change all overhauling kit,we put sleeve,we replace pistons,piston ring,valves,we refaced cylinder heads,but when we start and run the engine,drive and use it about a week,the trouble appears,sometimes the engine stall when the temperature reach before 1/2 of the gauge,sometimes when you shift the gear,when you turn on the aircon ditioning,when you make a turn,but mostly when the engine temperature reach that level........hope for your kind and respectful professional response,thank you and more power to your site.