Rpms causing shifting too early....2012 Cascadia

One truck with a super ten would give me 55 at about 1400. If you opened her up to shamble along at 75 in top gear you are pretty much redlined. It depends on the gearing back there in the rears. The ones that do mountain work really well.

Then there are those crappy big cams on tall 9's and 10's where you are already past 30 going into high range from low but frankly did not have the horses reserve to stay at speed limit in top gear. Something like 1450 give or take.

 

So... You used go 35 mph at 1500 rpm in what ever gear... Now in that same gear you go 25 mph at 1500 rpm...

Does the engine sound like it is turning 1500 rpm??? This is why I learned to shift by sound... Not rpms and speed. Not that it doesnt need fixed, because it does... But if yo just shift by sound and feel is your speed any different than it was before this problem???