Is this hard on engine?

My first thoughts on this, how are the adjustments on the baler. I've never run a NH wire tie, but do have a lot of experience with NH twine baler. When I say adjustments, I'm thinking plunger settings and plunger knife condition. My experience is if plunger and knife are in good condition and the material being baled is dried well, you cant get enough material through that pickup to cause a 300 much sweat in 3rd gear. With those NH pickups that is one H@$$ of a lot of material. I've seen enough material going through there you never saw a pickup bar or tooth. In my days of baling with 300 and NH S-69, the only reason for using TA was wet material, rough ground, poor or uneven windrows or just pickup couldn't handle volume. New Holland balers will make good 30" bales making 3 plunger strokes to the bale. Remember I didn't say excellent bales. Baling is not a building block competition. It's about harvesting the crop when the weather is good.

My bet is dull plunger knife is the cause for 300 bellowing.

Personally, if you need the TA every 30 seconds either leave it back, or shift down a gear. Why do you want to shift that much anyways?

The baler you mentioned has a plunger that does the compacting of the hay into the bale chamber and packing the bale. This takes a lot of power, so there is a flywheel that in the driveline that “absorbs” energy from the tractor when the plunger is moving out of the chamber and “transfers” energy to the plunger during the compression and looses momentum. What you are hearing is the governor on the tractor opening up trying to bring the RPM of the flywheel on the baler back up to speed.

Working an engine at rated RPM or varying RPM’s that peak out at rated at least for a moment or two don’t really hurt that engine other than the wear and tear on the governor and linkage. I'd be more concerned about the live PTO tube and hub in the back of the pressure plate. My dad used to square bale and had problems with this often.

I agree. Let the governor do its job with the PTO.