Why oh why do people persist in using ancient bipolar H-bridge chips such as L293, L298 and SN754410? These chips have high voltage drop, which also means that they get hot and can't take much current.
My advice is to forget bipolar motor driver chips and use modern mosfet-based chips instead.
If you really want to use a bipolar chip, then read the datasheet to see how much voltage drop it has, and increase the power supply voltage over and above the motor voltage by that amount.
If you have links to a good replacement MOSFET-based h-bridge driver chip in a thru-hole package variant that compare to the aforementioned bipolar devices, please post a link or some part numbers - I'm sure that tons of people would appreciate it!