My 2001 Dodge Ram 1500 5.9 sport vibrates and makes weird noise after 40 mph on a steady climb. If I am getting on the truck all is good it only happens when I am slowly increasing. I replaced the air filter, spark plugs, cap, rotor. No codes are shown!

Has this happened to anyone else? Any suggestions?

 

Hasn't happened to me but could be a misfire. A lot of people around that cruising speed report vibration and it turns out to be a minor misfire. Check engine light come on?

 

RPMs too low in OD (lugging the engine) causing pinging?

Sound like marbles rattling around in a coffee can?

Fixed your plenum yet?