Bigfleettech, yes fix was never posted! It bugs me when I see so many posts with answers to questions but no follow up. I left that place for a road job soon after the post. The other tech called the tennant guy, and found one plug under the intake manifold blown out, like someone else pointed out here.
From all the back firing the mixer had to be changed. BTW, I was able to buy a lot of parts from GM, like timing belt and water pump without waiting on tenant.