I've been where you are so I understand completely. I would be very surprised to hear that it's the voltage to your motors causing the issue. Here's what I can say from my experience-it's usually the simplest things. While there is tons of great info on the forum it's very easy to get lost in it all and overwhelmed.
Check the basics of the machine, belts, eccentric nuts, and pulley set screws and slow down your feed rate. I made thousand of dollars worth of product on my machine before doing any of the mods or adjusting the potentiometers, (basically because I had to- Christmas rush.)
Things weren't perfect and I had to cut slower than I wanted to, but I was able to get the job done.
I kept reading the forum and asking questions but I still only took on what I understood at the moment.
Only recently did I have to the time to do the gantry mod and then only last week did I adjust the voltage to the motors. Both things made a huge difference in accuracy and speed, but they weren't necessary for the machine to work, they were improvements. Before these upgrade I never cut above 40 in/min. And while that was slow and conservative it got the job done and I learned.
Also, I'm not suggesting you wait as long as I did to improve your machine these task really are pretty easy, I'm just saying take your time understanding your machine and the reason for the mods so you will better grasp why are you are doing and what it is supposed to achieve.