2002 3.0V6 surging at 3500 rpm
I have 2002 ford ranger edge with 3.0 v6 manual transmission with cold air intake other than that its bone stock. a few months ago my truck started surging but only after it has warmed up and only at 3500 rpm. if you accelerate hard through it it only will last for approximately 200rpm then go away. It happens in every gear and will vary slightly where it starts in each gear. It doesnt happen at all when the truck is cold or if I have been driving it for over an hour. I have replaced the fuel filter and the plugs arent that old. they are the two prong plugs so they dont have to be gapped. Ive checked the plugs and they look normal. The truck doesnt overheat at all it warms right up to normal and never wavers. I have done some searching but cant find any problems that resemble the one I have. Also I have no codes or check engine light. I was thinking it could be a clogged injector or maybe some sort of a bad sensor. Does anyone else have any thoughts or tests I can run to try to narrow it down? Does anything about the motor change around 3500 rpm? Does the motor kick in the vacumm advance there or something? thanks ahead of time for any help.