At a tournament one of my teams was having issues popping the motor controllers in the drive base motors. He had the 393 motors rigged for high speed at 160 rpm. He changed the motors back to 100 rpm and they didn’t have any problem. What if he set them at 160 rpm but we reduced the speed in the program, so that the bot is running at say 130 rpm. Will this work? Will the reduced torque we get at 160 rpm still be the same or is it just the speed that would change.
The torque will not improve at all with this setup. Adding more power increases speed and torque, so going with the HS-393 and reducing the power will reduce the torque as well as the speed.
What you really want to do is gear down the motors physically. So start with the faster motor and use gears (or chain+sprocket) to reduce the speed. This will inrease the torque proportionally. (Edit: You could also do the opposite and start with the slower 393 then gear for slightly faster speed.)
Here is some useful info about motors, and here is more background info on the issues you are having.
Another fix is to use a 6-motor speed drive instead of 4 (I assume you are using 4 because there typically aren’t issues with 6.)
Thank you Daniel that helped explain some things, appreciated
Glad to help 
Torque is always better then speed, on the safe side! 
Not necessarily, if designed well speed can increase robot speed without hindering performance. I have also found intake rollers are better on speed.
Not at all. Some (rare) situations require torque. Otherwise, you should go as fast as you can without burning out your motors. Speed gives you more opportunities to pick up objects, get around defending robots, and score. With the object limit in this year’s game, moving slowly around the court is going to kill you in Finals.
be on the win side 
In toss up, speed is the difference between a just ok robot, and a good robot. It can be the difference between winning and losing.