Last time we took our Pred-90 out (doing donuts on the ice), its engine "sputtered" at its top end. Checked the plug and it was loaded with carbon. Signs of too much oil. I also installed a hotter plug as well. Raptorlegs pointed out that I was running too much oil in my gas. I'm thinking the 10 degrees below freezing and lack of cold weather jetting had something to do with it as well.
How's your plug look? It should be beer bottle brown. Is your temperature dramatically different this time of year as well? Each of these things have an influence on "dies at top end".
To read your plug, surf:
Flush your system with fresh gas. Backfiring / burping is usually caused from bad gas or bad wiring. But, can be influenced by other things as well.
** On an E-Ton brand, I also once read about their Spark Arrestor / Muffler being full of carbon. You may want to check that "carbon & crud" holder on your unit as well.
If you think it's electrical problem, you could idle its engine and bring your it to a low warm state. Then, take a garden hose and spray all it wiring. Start from the bottom of the unit and slowly work your way up. If its engine starts to sputter, you found where an electrical fault "could be". This garden hose with spray sometimes finds electrical problems.
If external water can't find it, then its probably an internal electrical type problem. Change the plug, and swap out the coil with another Polaris coil. In the my old days, I had a set of plugs where one of them randomly stopped working at its top end. Took me over 3 weeks to find that problem. Hopefully, you've tried another plug and plug cap. And, hopefully you have another Polaris around that you can start swapping parts with. Those intermitting problems are always the hardest to find.
Hope this helps as well....