I THINK those are "nominal 4.5V" motors that come with that chassis, at least the ones I have are... They were VERY slow with 4.8V and a bipolar L293 type driver, MUCH better with 7.2V battery
See:
The DAGU Support Site (Thanks to Russell Cameron): https://sites.google.com/site/daguproducts/
The Motor specs: https://sites.google.com/site/daguproducts/home/motor-and-servo-specifications
The motor I THINK you have: DG01D.pdf - Google Drive
Check your wiring totally over (I usually remove it all and start over at this frustrating point)..
Also, test run the motors directly from the battery. Run OK??