Hey Jack, I have the same motorhome and will share what I did. I switched out the injectors with a set from Red Oak Diesel/Stan's the owner. I also added his torque plate to complement the injectors. I further blocked off the sensor line from the turbo to keep the waste-gate from opening. This took my boost from 20 to 30 lbs. With all this I went from 190 hp to 350, and the torque is awesome. From 475 to 750 ft. lbs. I did loose a bit of fuel milage; 9.5 to 8.5 MPG. But my ability to tow and climb is so much better.
My next venture will be advancing the fuel timing from stock 11 to 15 deg. This will up my fuel milage a bit without sacrificing power.
When driving the motorhome around town empty, you cannot believe how it accellerates! Once I'm in second the motorhome pulls strong!
About the transmission, I'm convenced your Allison is one if not the best automatics available for this application. About the torque plate, I did try to move the torque plate, wasn't enough gain for me. About the air inlet, if you have a wire mesh in the inlet, remove it. The filter is fine on these motorhomes e.g. 8" inlet, 25" long filter with lots of available surface area.
The exhaust is not bad on these either, pipe is 4" and 4' long and has a wide u-bend with a 12" radius. I did replace the muffler with a free-flowing one. No baffles just a 2' straight-thru muffler. Nice and quiet thanks to the turbo.
Have fun and good luck!
