Hi!

There is nothing unusual about a clutch slipping in fourth gear or high gear as it is an one to one ratio!
The higher the gear in the drive train the greater the disadvantage it has reduce load onto the engine.

This means there is no torque gain but a loss of RPMs. The engine RPMs are going directly into the rear differential from the transmission.
One turn in get you one rotation out of the driveshaft
Where as in first gear the engine makes like 18 turns to get the same one turn output. I just picked a number! (:)

With clutches it’s the same question!

If you checked the fifth gear, or overdrive, it will also slip and maybe even be quicker but you have to expect, not to feel the response to be so dramatic as you should be over 45mph to use it!
The engine gets about an additional 20% more load than a high gear does?
It’s why it’s called the over driven gear mode!

To check the clutch put the transmission in second gear or maybe third and drive the car up against a wall or tree. Try to take off and If it slips without killing the engine then you are experiencing a slipping the clutch without that wonderment you have in fourth.

Here the loss stops at a 3 to 4 turns of the engine to one turn of the wheels. The size of those wheels gets to be another calculation and the concept of actual horsepower delivered to the rear wheels get involved!
What’s USEABLE is where the stupid buying consumer gets beat to death or lost!
Once the tires break loose and burns away traction, the actual physics and math goes nuts!
Taxable or drawbar horsepower, are terms forgotten dealing with dead load pulling forces of a horse!
They had their place before todays marketing games of using brake horsepower!

When You are driving and experiencing this “flare”, the mass of the car is moving a long, it has an energy built up in it by “motion.”
This variation fades in and out, in so much, as a flare shape or bell curve in engineering, could work as a mental concept!
Pumps and fan designs use a “bell curve” concept to track efficiency at certain speeds.

The term “flaring” is very new to me!
Interesting analogy or choice of a word description to describe a feeling of something not normal as the other gears.

How did that term get started in your neck of the woods?
In mine, it would be something like this?
A trumpet player uses a cone or cup in its “flare” to change the sound.
I’ve heard it called a muffin because it looks like one and it muffle’s the sound.

The term “squishy” might be related to squeezing a not so firm tomato or a wet rag!
So, I guess it depends on what your “kitchen environment” was when we grew up!
Us boys, got to do the dishes! (:-)

To each, it’s his or her own mind set!

Phil