I've got three International 4900 with Dt466 power. These are Iowa state DOT trucks that I've purchased for snow work in Mass. One of the trucks has developed breathing issues. Its the 93 with an automatic trans. The truck has 170,000 on it to date, motor runs nice, sounds great running but had lost power when under load. Empty with no plow on the truck would not get past 30 on the flat, 15 was top speed up hill. Replaced the inter-cooler, had a hand full of pin holes init. New injectors last spring. Fuel filters and air filters. Still no improvement. It was pushing out a lot of smoke with no smell of fuel, showing a lack of air into the motor. Pulled the air filter out and the truck rolls nicely. Push two 11' plows full of wet snow at 30 mph. Not happy doing it with no air filter but found it necessary the other day. Any thoughts on the situation?