It's normal for a vehicle to drop out of overdrive when it's under a severe load like going up hill or a lot of weight in it. That helps the engine to maintain speed and keeps the transmission from running hot. The ECM moniters the actions of the car and driver inputs and makes a decision automatically.
not overdrive... it depends how fast ur going
Gravity.
Is your oil level?
because it is going uphill and the engine has to work harder?
Bad spark plugs are plug wires.
The overdrive should be switched off when you want to avoid unneccessary shifting. If you are driving on a hilly road, the vehicle will shift out of overdrive going uphill to maintain speed while pulling the vehicles weight up the hill, and shift into overdrive going down the hill to save fuel when additional engine power is not needed. When towing with an automatic transmission, the vehicle may tend to repeatedly shift in and out of overdrive due to the added weight. In scenerios such as these, you should turn off the overdrive to avoid the unneccesary shifting which puts more wear and tear on the transmission.
The CV joint being loose is one of the main causes for a car shaking while it is going uphill. However, a faulty AC and faulty engine could also be the problem.
the tilting of the bike causes the floats in the carburator to rise wich cuts off the fuel intake
No the can go faster downhill or uphill
It requires extra power to go uphill, against the pull of gravity.
downshift
Is the vehicles transmission downshifting to a lower gear as you go uphill? If not, that would be your first place to look. After that I would suspect that your engine timing is not autmatically advancing as it should be.