I will describe the 8 pins to match the code here:
Uno D2,3,4,5 go to the L298 motor IC like before
9,10,11,13 go thru 1k RES to 2,3,4,5
There are 4x 1uf CAPs between GND and 2,3,4,5
It's a really simple circuit, times 4.
I realize 13 is not PWM, that's a bug, I should use 6 instead, but I have not fixed the original code yet.
This circuit allows the PWM pins to create a smooth voltage with the appropriate time constant.
To use PWM in the code you have to change pinMode of 2-5 to INPUT.
When you change it back to OUTPUT, the maximum speed is not reduced.
I will try that, thanks, have you received my PM?