What RPM should I shift at?

The correct answer is...........

IF you have or can get a dyno curve, either for the engine or chassis, OR if you can muster up some sort of performance instrument like the old G-tech, or "I'm sure" there are now smart phone aps for that........in other words something that gives you an acceleration curve.

So you can use a curve for HP, for G force, or for torque. If you cannot generate curves for all gears, then pick a gear that is convenient and endeavor to do an accurate curve in that gear, from below the peak by far, to about as high as it will rev, in other words PAST the peak.

Plot the peak, and then plot the other gears using math to multiply the gear ratio

YOU WANT TO SHIFT where the curves for each gear CROSS

Here see this old thread

https://www.forabodiesonly.com/mopar/threads/maximize-shift-points.253427/
What you are gonna find is that for some gears you will be shifting at HIGHER RPM than the HP peak because even though you are past the peak, you will still accelerate faster in that gear at that RPM range than in the next higher gear with whatever the RPM drop is, because the engine will be off the curve so much. "It varies." "It depends"

This is overly complicated
https://www.evodynamics.com/blogs/news/114447365-calculating-shift-points