5 Speed swap

DionR said
While I don't completely disagree, remember that above stall the TC isn't going to slip. It might allow for a 1000 RPM "flair" when gently rolling through an intersection, but it isn't going to do that when it shifts at WOT. Unless I am ignorant of something, at best a TC is only going to slip maybe 5% above stall, if it a loose TC.

And a clutch can be slipped, too. If anything, I would expect a clutch to have more of an RPM flair at WOT that a TC will unless the stall is really high.

I've got to add that for most people how an AX15 with a tall gear might drive is an opinion based on theory (myself included), but for @75slant6 it is an opinion based on experience. Doesn't mean that for someone else it might be less than they hoped, but he has at least done it and can say how it feels to him rather than what he thinks it might feel like.

The slippage from a torque converter gets pretty complicated (or I guess, more complicated) when the output side is spinning. The stall speed indicates the max RPM difference between the input and output when the output is stopped but that doesn't mean there isn't still slippage between the two sides once the output starts rotating. The slippage rate is proportional to the difference in RPM and load/torque between the input and output. The slippage is at its max when the car launches then decreases as the car accelerates but never fully goes away; once the transmission shifts to the next gear and the output side drops in speed and increases load the slippage increases again. So basically that difference in percentage of slippage between the top of the first gear and bottom of second gear will reduce the RPM drop somewhat compared to the drop in a manual transmission. Also the momentary spike in load on the output side as the gear change occurs reduces the initial engine RPM drop a bit.

With a manual there is zero slippage through the clutch during a gear change, IF it's performed correctly. There can be some slippage due to driver technique (back on throttle before clutch pedal is fully released), if the clutch is too weak to handle the rotating inertia of the engine or if the engine spins down too slowly and doesn't match the trans input shaft RPM before the shift is completed. I figured out how to get rubber on the 1-2 shift in my Jeep by flooring it to redline, shifting quickly into second gear then dumping the clutch without needing to use any throttle because that 4.0L was so slow to spin down and had a lot of rotating mass with that 7-main-bearing crank. The factory clutch in those is also very "grabby" and doesn't like to be slipped much.