that's so cool! funnily enough, i actually originally designed the game to have a joke "reverse" challenge mode, wherein the truck would be stuck in reverse gear. there was a kinda-sorta-secret interaction mechanic developed specifically for that mode, which allowed the player to "shunt" the truck by pushing off nearby surfaces. i eventually dropped it though because it was interfering too much with regular play (people trying to pick up boxes off the ground then miss-clicking and launching the truck up into the air). very cool to see someone else naturally arrive at this challenge mode.
as for my best times i'm afraid i don't know, and my save file is unreliable due to various cheats i've left in the game for debug purposes ;) i'll do another run sometime soon and see what i can crack out!