LS power
Most are powered by GM ecotec motors. Great little motors: really good power to weight ratio and easy to package
Those cars are also running portal axles which have additional gear reduction in the "hubs". A normal trail car has gear reduction in the transmission, transfer case, and differential; these have all of that plus something like 1.8:1 in the "hub" as well (portal gearbox). Plenty of people trail wheel them, you just have to use higher gears to overcome the additional gearing. Since these hills are all close together most people dont take time to shift running from one course to the other.