2001 2500 Diesel Trailer Tow--4. 10 axle The engine is sluggish in 3rd and 4th gears. In 4th the engine jerks, on the slightest rise in the road and sometimes downshifts. I changed the oil and filter today---fuel filter and transmission filter changed within the last 6 mos. When I cycle the key 3 times I get P 0500 & P 1693. Please tell me a quick fix. we're planning to leave Sunday with the 5th wheel.