The diff is a problem with rubber tires, especially so with Pardus as they are heavier than Pits. You really do have to run the diff tight or you will slip the diff off almost all the corners.
I didn't like the stock diff rings as they seemed to require way too much sanding to get flat. I put some CRC rings on that seemed a little better. I also was able to get a slapmaster thrust to work. You have to use the medium sized spacer he sells. The other thing you need to do is cut down the plastic diff nut so it doesn't rub on the diff cap and unthread itself. I won't say it solved all problems, but it seemed better.
Lloyd- Run the pack forward and run a stiff center spring. Like I said, I was all over with the shock, but at the end of the year I ran a really stiff center spring with the battery forward. Also try reducing front droop. I don't know how you set yours, but I use a Team Durango screw td701001 which has 1.5mm wrench hexes on both ends. You can adjust the droop from the bottom of the arm in small increments.
Also, how do you have your ackermann set up? Are you forward or back on the knuckle?
As far as asphalt, I would go with either the old F104 Tamiya kit front tire or the Pardus front. They will balance the car out a lot better.
And minimal rear droop will probably help too.