Thanks for the responses -- it turned out to be a temporary glitch of some sort, because when I went back in a few hours later, the truck was very fast, indeed, as several posters noted above, faster than it used to be, it seemed to me. But for a while there it just could not move uphill. On a truck related note: I noticed that upon returning to the (now much faster) truck, the gas meter showed the tank as being full, whereas when I logged off it was only on half. I have not noticed that before -- is it regular that it fills itself after a while?