Overheating after screen replacement

So this will be the second Lens/LCD assembly we've ordered for this device due to the first replacement screen cutting off randomly and getting hot while turned on/charging/post testing device. So we ordered a new Lens/LCD assembly expecting a defective part on the first go. Round two, I've made sure to move all the protective tapes from the old screen to the new assembly and any other pieces of components that were in the old screen but not the new one. The phone is still heating up pretty seriously and cutting off from time to time after everything is put back together. Am I missing an important step that's causing a bad ground resulting in the overheating issue? At check-in, the receptionist made note of slight heat coming off of the device in its original condition, although the customer vehemently says overheating was never an issue. Anything would help. Thanks