So - you're asking why your Leopard is turning over so much? I kind of forgot the point in the middle of this thread somewhere.
The short answer is "any number of reasons".
Hopefully, information that is useful to you will now follow.
D plastic - it is likely that you've taco'ed your Leopard into a few trees. A couple full power drives into a tree with "non-premium" plastic can severely alter a discs stability. An understable disc can become "never-ever fade back" understable after a couple good whacks. However, this can be a good thing.
There's a good chance that you throw your Roc differently than your Leopard, even off the tee. Make sure you're not trying to crush that Leopard as hard as you can. Relax your reachback, it's amazing how far a disc can fly with seemingly no effort. To clarify, you MUST relax your reachback to avoid tensing your forearm muscles. When you're trying to huck your driver as hard as possible, you often block yourself from doing just that.
You said you were throwing 250' or so. Maybe you're throwing a little bit farther now? If you take Joe's Universal Flight Chart as the gospel truth (I certainly do), a Leopard SHOULD start acting differently - especially if you are throwing 20 ft. farther on AVERAGE. That average thing can be important to any of us who aren't really hitting it.
The power requirement for a Leopard, averaged across all tested plastics, is in the 225'-275' range. The distance you can throw when you start to CONSISTENTLY hit cruising speed for any given disc, is going to be slightly higher than the distances you regularly throw. E.g. if you CAN throw 290', you can probably CONSISTENTLY throw 260'. However, if your max distance is more like 250', you might regularly only throw 225' - which will likely not translate into enough acceleration for the disc to fly as intended.
If your max D went up 10-20', you may now be consistently getting that Leopard flying faster. This gap between max D and what you consistently throw will obviously become less significant the better your form becomes. Are you throwing your other discs farther than you used to? (more importantly, are your SHORTEST drives going farther than your shortest drives used to?)
People asked you for info on the flight path of your Roc. I pointed out something that (currently) may be a problem in this troubleshooting session - you might throw your Roc very differently from your Leopard.
That said, a lot of people are intimately familiar with how a Roc acts at any given distance/power. I am not one of them, but they can certainly help you out.
I would suggest two things.
1) leave the Leopard at home and play some all Roc/Aviar rounds
You'll get used to the Roc, it will make you pay closer attention to release angles, and you will have enough "data" to potentially get some useful advice from all those Roc lovers.
2) Learn to hyzer flip the Leopard. Preferably in a field at first. I would say take your Roc out there and throw both - learn how they're different, and how you can get them to do the same things. You might not want to just throw the Leopard over and over - you may find it difficult to adjust back to flat releases if you haven't been playing long.
A 137g Shark is WICKED light.
The weights you listed in your original post are fine, but a 162g DX Leopard is on the lower end of what most people throw. It's probably pretty flippy now that you've worn it in so you'll need to learn to hyzer flip it for straight / turnover / s-curve shots. Upsides may include versatility, throwing huge anhyzer bombs and trusting that it won't flex back, a potential roller disc, or something to throw over water hazards (if you ultimately decide you don't like it) =)
You will probably have to change everything you learn, multiple times. I recently blasted through the 300' barrier, and although it feels great, I know I've probably added other problems that will keep me from 420'. It's a long process, and can be extremely frustrating. Just remember to relax and have fun.