Paymaster, my honest and rather serious suggestion is that you obtain a real, confirmed weight for your 26' trailer, automobile, and any other support gear loaded. Get it on a scale and find out.
If it is anywhere near the 10K pounds you first suggested, then you'll need a different, heavy duty tow rig to haul it safely. Maybe your rig is at or below the proper tow weight limits, but you'll never know until you do something other than guess. A quick websurf suggests the Cobra is in the 3,600 lbs range, as are 8.5'x26' car-hauler trailers for a minimum of 7,200 lbs before liquids, occupants, and other equipment.
Worrying about MPG while towing such a large load is analgous to texting while driving. Focus on the real issue for both your and other's safety.
Others have already suggested you not tow such a load with the Jeep Grand Cherokee for good reason. I would also bet you burned through your previous truck's transmission due to being overloaded.
Please understand that I am not trying to deliver a lecture or be a jerk about this. You are getting good advice throughout this thread.