GP4 TSM performance

My GP4 runs fine with the original 17 tracks but is very sluggish when running a custom track set through TSM. Tracks take three times as long to load and a race will not make it through 15 laps without stopping and throwing up a black screen. Strange thing, it does not abort the race or the game totally, it's as though the pause has been hit, the GP4 icon is at the bottom bar, you may click on it and it will pull up the screen with options to save or return to cock pit, doing so displays the pause screen. I have two sims I use (mine and my sons) both Windows 7 machines w/good processesors, RAM, and SSDs. Both behave the same exact way. I have set the virtual memory high on both with no change in results. Advice?