Hello again,
I am currently talking with someone from Panic to try to figure out what happened to cause slowdown after a system update.
Until then I made a slightly more optimized version of the game that will be more playable. The menus should be more responsive. However, the map screen might still be pretty slow but you can still experience the game until I figure out a more robust fix.
The download is titled Heavy Trucking 1.01 (temporary slowdown patch).