The two buses are great. However, the 40ft bus is way too underpowered for use on any other map (unless it is flat) Is the bus like this in real life?
The short answer is yes, but to better answer the question, I took one of these buses to Poland.
I drove one of these buses on the wonderful Projekt Szczecin map*, and in particular, an incline on the 63 route at Artyleryjska. I drove to the bus stop there, then attempted to drive onward, toward Skolwin. The only way I could do this though was to set the parking brake, rev up the engine, then while doing so, release the brake. Inspecting the incline in the editor revealed that the incline at the Skolwin-bound bus stop at Artyleryjska is 8% (1 in 12.5). I wasn't able to go faster than 25 km/h until the incline began to level off. Keep in mind this was with an empty bus!
I then considered a real-world example of bus operations on steep inclines, in particular steep inclines on bus routes I've traveled on. The Bx9 route in New York City has an example of such a steep incline between Heath Avenue and Sedgwick Avenue on Kingsbridge Road in The Bronx. Here, the elevation of the road changes by 39 meters in a distance of about 400 meters.
Here is video of a particular trip aboard a bus on the Bx9 route. The bus used is a New Flyer D60HF, an older high-floor diesel variant of the DE60LF included with the Chicago add-on. Watch the speed (if you want to call it that) of the bus, and the sound of the engine as the bus makes its way up.
New Flyer Artic #5281 Bx9 Bus Ride on West Kingsbridge Road
So yeah, if you send the bus up a steep incline, it's going to struggle a bit.
* I know the Tettau map has some steeper inclines (up to 15% according to posted signs), but the thought of negotiating those narrow winding roads in the D40LF made me dizzy.
EDIT (2015/08/10): Drove the D40LF in Tettau. Do not recommend it, especially on the 8342. While climbing the mountain to Kronach, full throttle, the bus actually started going backwards, down the incline. Had to drive swerving back and forth across the road in order to keep climbing, and even then, it wasn't going faster than 10 km/h at full throttle until the road leveled off a bit. There was another point on the 8343 where I managed to get the bus going 70 mph downhill, only to slow to 10 mph by the top of the next upward incline, again, full throttle the whole time.