With the engine off, try spinning the auger, it should spin pretty freely. Sounds like there might be an issue there.

This condition is most severe when running on high (rabbit). When running a bit lower the issue only happens during heavy snow load.

Has any maintainence been done like putting grease in the grease fittings etc. Do the simple stuff first. Put some grease in the fittings, check the diff fluid level. If those are good, I would check out the belt and check the tenion. If that seems fine, remove the belt and try spinning the auger. Maybe the auger differential is shot. If it seems normal, maybe you need to replace the clutch. Did you hit anything with the augers and possibly bend something?

Sounds like the fuel mix is running a bit too lean.
Check for vacuum leaks on the carb/intake mounting.
You might also throw a good dose of carb cleaner in the tank and hope.

Thanks for the replies. I will start with the simple stuff and report any improved or new symptoms.