Running with my Cat

I keep telling my wife that I need to stop running with my cat Clifford. See, Clifford is a nutty cat that has some mental issues. One of those issues is with food, which makes him a hefty 17 pounds (last time I weighed him). He's been on a diet for a few months now, but I don't see an improvement.
I'm a slow runner. A 10 minute mile is comfortable for me. I can and have gone faster, but a tempo run of 10 mm I can do for a long time. I have already set my 2011 goals and one is to run a 5k in under 23 minutes. I really want to go sub 20, but I thought 23 is much more realistic. I've only been running since...August 22 (I just looked it up) and have moved my 5k time from about 39minutes (my first time running the distance) to 28'06. Huge chunks of time were cut off at times- one time I beat my PR by 5 minutes.
Anyway, I need to cut off another 5+ minutes. How can I do that? I know I need to improve my efficiency, but that will come with the miles. another part of the plan is to stop running with my cat. I'm probably an average American weight, so that means about 15-20 lbs overweight, about the weight of Clifford. So if I can lose the cat on my runs that should drop another minute or two. I started out running at 178 and am now down to 166. I think 145-150 is a good weight to try for. Hopefully I can hit my target by about March/April.