Hi everyone,
I'd like to give an update to this problem I was having with this engine. Over the weekend I met up with Lou1985 and we took a look at the two BNSF GS-4's. We determined quickly that both engines were mechanically sound. So with mechanical and linkage binding being ruled out, we decided to try reloading the sound file. Once the sound file was reloaded in both engines, we tested each engine out and they both ran great. There was no stuttering at all under 10 SMPH.
Now that both engines are running well, I'd like to thank everyone that responded and offer their expertise. Big thanks goes out to Lou for offering to spend some time helping me out with these engines. I really appreciate it.