Some Allisons are better at handling power/tq than others. Most can handle 75-90 additional hp without a lot of complaint, some can't. Assuming the ATF level in the trans is where it needs to be, you may have but two choices: 1- run no more than the lower Diablo power setting. 2- Put some money into the transmission.

A couple of years ago I communicated with a member who's 2005 LLY Allison was setting trans codes when using 60 or more additional hp. This particular trans had set a code early in its life at the stock power setting, so it was likely not up to par from the beginning. Towing heavy with 60hp pushed the owner into a performance trans rebuild. Then he was happy...

Jim