I have 2000 Dodge Van 2500 5.9 with only 37k miles. Having issues when I step on the gas between 15 -40 mph or stomp on it to get on the freeway between those miles the engine bogs down on power. Almost like a diesel engine sound. But once it is over 40 no more issue. I can do 90 on the highway without a problem. Changed fuel pump, did a tune up, flushed fuel injector, Now I have taken it to a mechanic they tested pressure on the regulator and it is fine. Still no difference, HELP. The mechanic now wants to start fishing at my cost he is telling me the Catalytic might be bad but I'm not having any other problems that would warrant that. I have plenty of power after 40mph. But he is telling me he would need it for a couple days at the cost of about $500-$700 for this privilege, Maybe more.