Our HR 34 PDD was equipped with the 340 ISB/2500 Allison and was unbelievable. It always had 2800# behind it and I could never tell it was there. We only would fall below 50 mph if we got trapped behind a slow moving vehicle. It would however accelerate after being trapped unless the grade was extremely steep. When we moved our possessions from Los Angeles to East Tennessee I had our 7x16 enclosed trailer on the back. Judging from the tire wear when we got back to East TN I can tell you the trailer was severely overload (7000# gross) and the engine/trans combination handled it with no apparent decrease in performance.
Randy