Quote Originally Posted by Thymeclock
Unfortunately, when there is traffic it is impossible to break 45 – thus the car is spending most of its time in first, second and third gears at best, and it virtually never goes into high gear, which would yield the best fuel efficiency.
Presumably when you finish accelerating, to let's say 40 mph, you back off the throttle from 35 TPS to cruise at a constant speed, and your TPS value would drop.
Of course, the TPS reading does drop as you press on the accelerator less.

Are you saying the transmission still won't upshift at ~40 even with the lower TPS value at cruise?
No, it won't - but it makes no difference. It won't go into 4th gear at all until 45 mph is reached, no matter what the acceleration rate (which is gauged by the TPS) is.