I have two 1/10 trucks. Both have been great. Recently one isn't as fast as the other...25% on the throttle of one is faster than 100% on the slow truck. I installed new 20T motor in the slow one. Both trucks seem to spin the tires the same without resistance but that changes when placed on the asphalt. Suggestions? ESC? Although it seems more like some sort of mechanical issue like a clutch, etc. Also, what is the lifespan of the lipo batteries?