I mean just what itn say's i was going down the road and it started losing speed untill it was down to 45 mph, on a hill it all but stops i don't mean the batteries man this is why i posted here,nobody around here can figure it out.I am a pretty good mechanic in my on right ,just not a computer genuis and that is what you have to be to work on a mack. I had one of the best mechanic's in southeast texas work on it after PERFORMANCE MACK TRIED FOR 4 WEEKS but he works at a volvo dealership and dosen't have computer acess but he could check a lot of things and his last guess was the ecm after he did all he could.He even hooked gauges to check fuel pressure boost pressure.pyro tenp fuel temp, air in fuel hooked up a lap top and had another mechanic drive it down the hiway while he checked all he could But PERFORMANCE MACK is a authorized dealer they said that they removed the parameters and short of a overhaul that was all they could do. this truck only has 430,ooo miles on it -- it was running good going down the hiway all at once it stared losing pulling power and that what happened i haven't been able to restore power since. Runs good empty but add even a lite load (20 tons) and it does 45 on flat ground 25 on hills not mountains. hills i never have to down shift this pete i just bought making same runs i made w/ mack..i no it's a stumper that's why i'm here but if you can't help i do thank you for tryingn and your time it had a 10 speed road ranger but it pulled fine for almost a year