I have a 2005 GC 5.7 Limited which has a strange problem at low RPM (1200 – 1700) in 4th gear which equates to 40-45 MPH road speed where it has a very rough (jerky) response in this RPM range. In 3rd gear and in 4th gear above 1700 RPM is absolutely fine. The engine idles smoothly and I have no error codes, it’s just at low RPM in 4th that I have this problem, which also feels worse when going uphill. I have seen some suggestion that spark plugs leads might cause this type of problem and even some suggestion of the torque converter clutch, but wanted to see if anyone has experienced a similar problem. Thanks in advance.
Sounds like a xmission performance issue to me. If it were purely engine-related, you would likely see the symptoms under other conditions.
You didn't say how long you've been owned by this HEMI or its mileage. If you do not know its service history and there are over 60K miles on the odometer, I would start by draining the xmission and changing both filters. There were some problems with the earlier 545RFE xmission filters. This is a positive 1st step towards diagnosing the root cause (if it is due for service anyway).
Need to buy both filters, ~7 qts of good quality ATF+4 xmission fluid, and lots of shop rags.
Plan on ~$100 if you do it. My dealer had a service special for $145 for fluid, parts, and labor for this service.
Perhaps your local dealer has a similar offer if you are not inclined to do it yourself. [Of course, this presumes you trust them. In my case, that is not an issue.]
In the event that the xmission service does not cure the problem, then go after the ignition system (plugs and wires). Watch your replacement plugs: Either MOPAR p/n SPRE14MCC4 -or- Champion 570 with dark top center electrodes.
There is a StarCase on this, so do not accept MOPAR or Champion spark plugs with silver top center electrodes (where the plug wire or coil connects).
WK Jeeps recommends 0.045 gap and plugs tightened to 13 ft. lbs. My '08 MOPAR WK shop manual calls for 0.043" and 12-15 ft-lbs torque. Your choice.
recommends Taylor Shorty ignition wires. He can comment on this; the '08 HEMI's have a coil-on-plug arrangement.
I'd be interested to hear how it goes.
This advice may be worth what you paid to get it!