Just my $.02 here.
We have a 1998 C8.3 and while yours is newer, I would bet that it is an ISC 8.3 or an 8.3L.
On our coach, the authorized Allison trans rebuilder in our area (So Cal) looked up the specs for our specific combo which is rated at 275HP/800FT# and said that while the engine might possibly be able to be increased to 350HP with a Banks kit or similar, the MD3060 trans was only good for a maximum of 800FT# of torque.
Allison also makes an MD3066 (which is only determined via the serial number) that is good for up to 1050FT#. I asked what might happen if I added the Banks Stinger kit which changes our numbers to 350HP/950FT#. I was told that it could be fine but they had seen similar setups and all had to have their transmissions replaced with rebuilt 3060's or upgraded to 3066's. The cost is right around $7,000.
I suppose it depends on how you watch the EGT (exhaust gas temperature) gauge/pyrometer but remember that the older ('96-00/01) 8.3 engines are I believe all 12 valvers while the 5.9 ISB's are usually 24 valvers. I am not sure the 12 valve engine can safely handle the excess HP. Later versions of this engine, possibly yours, have stronger internal components and were uprated by Cummins. The key is to call Cummins, give them your engine serial number and ask them what you might be able to get out of the engine re: HP. I would do the same with Allison and the trans.
It is all a guessing game as many others have modified their engine/trans combos. I don't happen to have the $1600 for the kit (nor the $750 for the installation and dyno tune at Banks) and while I can install and "tweak" the kit myself safely, I am ok with taking a bit longer to get to my destination.
After all, I/we are on vacation when in the coach.
Sorry so long winded but I have only found one comparable coach to ours that did the mods so far. His runs great BUT if I remember correctly, you do have to watch the pyrometer on long hill climbs with a toad.
I am not sure when the DW drives it that she will remember this critical factoid as she is busy driving.