One thing I did not see in this thread so far;
For coffee-spiller shifts, you need coffee-spiller torque thru-put.
With a 2500TC, your engine is way down on the torque curve to start with,
and hiway gears, if you have them,will keep it there for a long time.
If your cylinder pressure is also down, it will feel like a limp-noodle. And no amount of transmission modding can correct for this condition.
Maybe the responders know your powertrain.....
Then you need more line pressure. Which will require more governor pressure, for the auto-shift part to work properly.
In auto-shift mode; the governor commands the shift based on the pressure the spinning driveshaft generates. The faster you go, the more pressure iyt makes.
In order for the governor pressure to not cause the shifts to be too early, two things need to be addressed;
1) the governor has to be tuned to the driveshaft speed, and
2) the line pressure has to be in the ball-park, so that the KD mechanism is tuneable.
In manual-shift mode;
the governor is ignored, so that line-pressure can run the show. How the KD works is by reducing line-pressure at reduced throttle-openings, so that line-pressure doesn't cause your kidney stones to drop into the chute....
But in order for coffee-spiller mode to engage, you still have to have a large torque input, and enough traction to not spin the tires right off.
Take a look at this stock 5.2Magnum.
Notice at 2000 the torque is ~275.. By 2500 it has climbed to 290, and at peak it makes a tic under 300.
At 4400 the power peaks at ~230, but notice the torque has fallen to 270, about the same as what it made at 1800 rpm.
The following description is for illustrative purposes only;
Suppose you had a 2000TC and 2.76 gears. The simple math says ; 276 ftlbs at the crank, times 2.45 gear in the trans, times 2.76 in the diff = 1866 into the rear axles. There is no coffee-spiller in that.
Now suppose you had a 3200TC and 3.91s; the simple math is 295 x2.45 x3.91=2826 ftlbs into the axles, which is 2826/1866= plus 51%; that's gonna spill the coffee! But here's the thing; the sooner(in roadspeed) that the trans hits second, the more violent it will be.
So, with 2.76s the engine will hit 4400 at ~48mph. whereas with 3.91s, that would be 33.6mph. On the 1-2 shift, the Rs will fall to 2600. The shift is more violent at 33.6mph, because the engine is spending less power to overcome the wind-resistance, so it has more left over to launch the car. But see here; on the 1-2 shift, 2600 is down to 140hp, from 230. If you had a 3200TC, the power would drop to just 180hp, that's a major advantage, and coffee-spiller for sure.
I used a big enough rear gear spread to make it obvious what is going on. From 3.23s to 3.55s is only 9.9% difference. And from 2600 to 2800 is only 5 footpounds so less than 2%. Furthermore, the 5.2M is a medium-compression engine with a small cam, indicating plenty of cylinder pressure. A smog-era 318LA will not post numbers anywhere near this.
Like said; for illustrative purposes only;
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