I replaced my capacitor and the blower motor is still over heating and shutting off. I have only the high speed wire hooked up with this 3/4 motor.

First off a 3/4 HP motor is large for regular HVAC units, It is possible you do not have enough supply and or return air duct to handel the air the blower will move. That will cause overheating.

Try lowering the motor speed down to medium or low just to see if that helps your problem.

NOTE once a motor is hot it will take some time to cool off. When you change the speed leave it cool for one hour before you try and test the lower speed.Last but not least you can take a amprobe reading and compare the current draw against the blower motor label.

Make sure all registers are open and the return air has a clean filter.

With the blower running does it sound like it is under allot of negative or positive pressure? It would make air noises like whistling. If so check your ducts and make sure you have properly sized return and supply, no damaged or crushed ducts and a clean filter.

A 3/4 hp motor should not be straining to move the air, is the blower wheel clean?

Sounds like you may have an air flow problem which can lead to overheating the motor.