Wow, this is an interesting thread with a lot of branches. Maybe all parties have found their answers. Seems the consensus is to change axle gearing or use the manual 3053.
My friend Matt and I have rebuilt one A3 AT 1545 with a melted fourth/reverse clutch pack that will go into the A3 4x4 project I have going. Matt (was) a certified Allison and GM tranny man but is on his own in a small shop now, kinda eccentric.
Joe brought his tranny up to Matt and again, we have a burned up set of frictions and steels and a ground away aluminum piston on fourth/reverse. This one got metal into the governor and made it turn like it has gravel in the bearing. That had to come from the locking torque converter, given the oil flow path.
The tranny that is presently in my A3 will be replaced soon with my rebuilt one, so I will have a third 1545 to rebuild (and sell or have to trade).
Back to the subject of the OP. Matt noticed that almost the guts to an Allison 1545 (and 545) will fit and are the same size as the GM 4L80E and specifically the fourth/reverse clutch is what is called the "direct clutch" of the 4L80E tranny. Matt told me many times that the steel piston with vulcanized seal in the 4L80E had much tighter sealing and better pressure than the Allison Aluminum piston, resulting in greater clamping pressure. Also, the 4L80E has much improved frictions and steels and spring.
The 4L80E "direct drive" clutch pack is vastly improved and has 40% more clutch surface area....and goes into the fourth/reverse of the Alison that is a major weak link ESPECIALLY FOR HIGHWAY SPEED and more so with higher gears.
That raises the question I have....is the 4L80E GM with overdrive, a similar and perhaps interchangeably option behind the 3116? I don't know the answer but never saw it mentioned in this thread.
Think about it....the goal here (of the thread) is more speed and a reduction of rpm, perhaps with an auto or as discussed, the 3053. I want to go 65 and be around 2500 or slightly less. If I keep the 1/1 ratio of the Alison, I have the option of sticking with the 1545 with locking torque converter or change to the 545 relatively easy.
Now we also have the option of having our locking torque converters upgraded from one to two or three clutch plates, further strengthening what has been viewed as the weak link.
While my rebuilt 1545 is going into my 4x4 project, the tranny that is in it will be rebuilt next and I will put the 4L80E upgraded steels, frictions, spring and vulcanized piston in it for 40% more clutch area and (guess) 25% more clamp pressure.
If you are going to get speed by buying Overson gears...this fourth clutch pack upgrade to the Allison is a must in my opinion....and wealthy can that multi clutch torque converter rebuild.
Plan for the A3 4x4 will add the 2 sets of Overson gears, air locker (rear) and lock out fronts. That's why I call it "money pit".
Here is one supplier link for the high performance clutch parts
https://www.transmissioncenter.com/s...rect-hp-64-95/
https://www.transmissioncenter.com/s...bonded-piston/