IIRC its the same type of setup with cross over tubes and if they are TQ'ed correctly issues will ensue. You have another complication in the VP-44 that will exhibit the same type of behaviour when it warms up.

Are you getting any codes or dead pedal? Best thing I found is get as heavy a load as oyu can and drive the snot out of it up and down grades until it throws a code or not. If you get a code and have low power its bet it will be P0216.