I own an 03 Dodge 2500 Cummins. It has around 150,000 miles on it. Performance upgrades include exaust, intake, and programming chip. Over the past year my truck has been gradually losing power and gas mileage. There are numerous things that I would consider a problem but I need to try to narrow it down. Here are some things that I think have changed since it last ran great. It seems that there is more smoke coming from the exaust than before. The truck is riding very rough at higher speeds, put only with my foot on the gas, it coasts smooth. When I am coasting, as I put my foot on the gas it is rough as it engages again. I have lost power and acceleration. My fuel mileage is 11-12 miles per gallon. Can you think of any ideas from this? I have replaced my fuel lift pump, I consistently change my oil and replace the oil and fuel filters, and clean my air filter regularly.