When I get on the freeway if I am running around 50 and I roll into the power I feel a vibration or a shutter if I let out of the skinny peddle it goes away. Any ideas what it could be or where to start looking?

Thanks.

 

Sounds like a u-joint issue. Look for red dust ( rust ) at the bearing caps of the u-joint, or feel for play in the joints. Have to have the load off of it though. Block the wheels and use jackstands when jacking up the truck. Put it in neutral and feel for any freeplay in the u-joints.

 

Might be your torque converter clutch. Mine does it too. I'm going to be replacing my TC and VB soon, so at this point I'm just not pushing it to the point where it does it (otherwise you get clutch material and shards floating through your tranny-not good).l

TC clutches slip when you're making too much torque for the RPM you're spinning at. The holding force on the clutch is the tranny line pressure, which is, in part, dependent on your throttle position, the input shaft speed (which spins your tranny pump), and the valve body. Essentially, at low RPMs, there isn't enough line pressure in the tranny to hold the clutch against the increase in torque that you've made because of the Smarty. That's why the clutch starts to slip-and what you feel is all that vibration.

The thing you have to remember is that Chrysler made Cummins down-tune our engines because they didn't want to warranty the driveline against the factory-tune Cummins. IIRC, when you have one of our motors in marine tune, it makes something like 450 HP and 850 lb-ft of torque from the factory. Chrysler didn't want to extend their warranty against that, because I think our trannies are only rated to something like 590 lb-ft of input torque. So, whenever you increase engine hp/torque (like with your Smarty), the Cummins can handle it-but your tranny cannot. At our stock truck tune, it's already maxed out at its torque-handling capacity.

JMTC-

Fitz