Since you have already purchased and installed the i7 ....
One would consider that the paste was cleaned off and changed as well as the fan(s) being blown out, new paste installed, everything back as it should be.
The i7 (even with the mobile models) has quite a bit more power draw than the i5. It is going to produce well more heat and should be considered to keep it on a flat surface or tray, etc.
You might be able to minimize some of the heat issues by changing the power state. If you haven't, you might consider a clean install, otherwise at the very least make sure you have updated the chipset driver.
The i7 is supported on the platform. Looks like they offered this model with everything.
Dell Latitude E5430 Owner's Manual | Dell US