It would be a transmission issue, not up shifting. If the engine is in "limp mode" it will not accelerate over a set mph.
A car traveling over 45 mph can hydroplane with about 1/10th of an inch of water on the road.
If you are driving for a period of time over 45 mph then use overdrive. If you are driving under 45 mph or in traffic that is speeding up and slowing down over and under 45 mph then do not use.
Type your answer here... If the vehicle is traveling at 45 mph, mph = miles per hour. In 4 hours it would travel 4 x 45 = 180 miles.
If your vehicle has an automatic transmission with overdrive, then at speeds above 45 mph, it should be in overdrive, which reduces engine RPM's to save fuel.
problem with your transmission in 5th gear
The first thing I would check is for broken motor mounts. This causes the vibration around 40-45 mph. There is a service / recall bulletin about this at Kia.
If you are on a highway maintaining over 45 mph. OK, but If vehicle continually shifts in and out of overdrive you are better off leaving it in 3rd
45 mph is 72.4205 kph
the termostat is broke..
45 miles is 72.4 kilometres. 45 miph is 72.4 kmh-1.
It would take 3 hours... to drive for 3 hours. Of course, if you mean 45 mph for 3 miles then it would take just over 2 minutes of consistent 45 mph to go 3 miles.