Sounds like the TCI is going bad and hitting the rev limiter, causing it to cut out/break up.
You could try the HEI conversion. Don't cut the factory harness, just run your own wires so it is reversible if that's not it. There's no way to test the TCI other than swap in a new one. A new one from Yamaha is $350 and they're not returnable if that's not it. Aftermarket ones are garbage, not worth your time to even try.
http://www.buggiesgonewild.com/gas-y...ml#post1498533
If you just temp use male spade terminals in the TCI/Ignitor connector, you should be able to temporarily install a chrysler HEI conversion at least to test. If it works, then great, you can cut/splice then to make it permanent, or order a new OEM TCI if you prefer. If not, just unplug, return, and we can continue with trying to see if something else is going on... But I'd bet dollars to donuts the rev limiter is kicking in and causing your issues.
There's no rev limiter built into the chrysler parts so I would recommend reconnecting everything back to the governor so you don't break the motor revving too high on accident...