I have a team that has created a drivetrain where the motors are hooked to gears, which connect to other gears. The wheels are not connected to anything. They just role. Students used a 4 wheel drivetrain set up to code this but the robot runs opposite of the code. I had them reverse the code and it is still not working correctly. I had them create motor groups instead, but they cannot use the joy sticks to drive, they have to use the buttons. Also it is very slow.
Any tips on programming or build will be greatly appreciated! 
Can you post examples of your code?
A simple drivetrain shouldn’t need code if you are using the V5 Blocks. Here is a link to help you get started. https://kb.vex.com/hc/en-us/articles/360037808332-Configuring-a-4-Motor-Drivetrain-No-Gyro-in-VEXcode-V5
If you have a drive train set up you can go into the controller in the device menu and click on the joysticks. This should cycle through different control modes for your drive train without any code.
You should then be able to remove your old code.
If you don’t want to do that it would seem you are using if a controller reaches a certain point. Just set that side of the drive train to the value of the joystick. Way simpler and gives precise control.
Also, make sure to add a block at the start of your code to set the drive train and drive turn velocity to %100 as they default to %50.
Also if it’s slow smoothing could be rubbing causing a lot of friction.
It seems you have a gear-down ratio to the wheels and this could be reducing the torque from the motors enough that it doesn’t have the power to get up to speed.
It’s a lot to unpack but hope it helps.