Wouldn't hurt to try the thermostat, if it isn't that then possibly the radiator is either plugged inside, or the outside of the radiator could also be plugged with dirt, leaves, bugs, etc. If you are driving it in town it could also be the electric cooling fan. Lots of possibilities here.

Something is stopping the flow of cooling water. If you have no thermostat, that leaves just the H2O pump that has been replaced---> loose belt maybe ??

Could they have installed a defective thermostat or put it in backwards?

Or perhaps a defective H2O pump ? Crimped or plugged radiator hose ?

check your coolant level. fill it up if it still over heats let it cool down then fill up the radiator again. if it takes a decent amount of coolant at this point you probably have a leak. if it dosent need to be topped off then you probably need a radiator flush which you can get done at a jiffy lube or a oil can henrys

Bad thermostat , low on coolant , bad hose .

I would seriously be thinking head gasket.