Rover goes crazy during Auto Missions

I am building a rover from scratch. I am using the Sabertooth motor controller with a pixhawk orange cube and rover 4.0 firmware. I finished this build around a month and a half ago and everything was working perfectly. I had tested for about two weeks using a tow behind mower and that was working flawlessly. However, yesterday I ran into a problem that I had never seen before. When I uploaded my mission and the rover took off to do it’s thing; it started going crazy. The rover would go to the first point like it should (it was a spiral path that I was doing) , then when it would go to make a turn, let us say the top right corner of the mission for ease of use. Once it would start heading towards the top right corner waypoint the speed would increase from around 2…25-2.5 mph like I had wanted it to to run the whole mission, but when it got close to the top right corner waypoints during the mission, it would speed up to around 4 mph and then take the turn super wide. This is a problem that I need help with but the main issue I am facing is that sometimes, randomly, throughout the mission, the rover would decide to veer off course and take a drastic left turn, then a drastic right turn and seem to get confused as to where the next waypoint was. I tried to repeat this again this morning and changed the cruise throttle parameter. After I changed this, it seemed to perform just fine again. However, on another run I did today, it seemed to fall right back into it’s old ways and speed up when heading to certain waypoints that would then mess up the path planning. Along with that, it would also randomly veer off path again and seem to get lost. If anyone could help me with a place to start looking that would be awesome. Thank you guys and sorry for the lengthy post.