You could either be in too high of gear or your (if manual)clutch might be going out.
Check the catalytic converter. They get plugged and cause the vehicle to lose power.
Belt
Fuel Pump problem or clogged converter
could possible be because there are gravity fed and the motor is gettin choked of fuel
Generally when we are going up hill because of the gravity pull, more power is needed. So when traveling uphill more power is needed than downhill.
You may have a blown head gasket.. Check the coolant overflow for oily, black residue.
A late oil change will not cause of car to lose power. Oil is used to keep the engine components lubricated. The lose of power may be coming from the car running to lean. Take to the car to receive a diagnostics test.
Try lose there power by
cos youre in the wrong gear.
They lose power and land in North America
When they move over dry land they begin to lose power.
Climbing long hills.