The Chevy 8.1 is a great engine with plenty of power. The Allison transmission is an awesome transmission. I cant compare the Allision to the new Ford trans, but comparing the Allison to the Ford trans they were using back in the era your looking at, is no comparison and the Allison kills it! You don't hear about people having issues with the Allison Trans.
Now IMO the Workhorse suspension sucks! They have a joke of a sway bar system. In order to make my my 04 Workhorse chassis ride as nice as my family members 02 Ford chassis I had to add aftermarket Bilsteins, rear track bar & real rear sway bar. I have been told adding a front track bar & or Sway bar is a big improvement. So IMO to make the Workhorse ride as nice as the Ford I had to add $1,000 worth of suspension upgrades, and that is not doing the front suspension.