gave up on castle a long time ago due to there bec failing on most esc i used.. tried a new pro esc but it would not calibrate to my forward on my radio.. what a waste of cash.. i think its your gearing.. try a larger spur if you can .. i think when you try to crawl its has too much resistance on your present gearing.. on a few crawlers i have i have as low as 10t pinions on 86 tooth spurs.. my crawlers are in the 6 pound range some have more weight..