I've got a 2005 SRT6 with 170,000 miles--and its been a great car. For the last 10,000 miles, I've noticed a vibration or "studder" from the powertrain when accelerating or going uphill (under load) around 35-40 mph....and also 65-75mph. Seems to be coming from the engine--slight loss of power.
I've check the tires and differential for vibrations, also fuel filters were changed, replaced the plugs/wires and also removed the exhaust to check for reduced back pressure. Everything is fine and no codes come up.
This studdering happens in any gear, 1st/2nd/etc. and air cond on or off, also no differences in summer or winter temps/humidity.....same problem.

Anyone out there have any ideas what might be causing this?