Harm balancer or motor mounts?

Getting the dreaded low frequency vibrations, heaviest between 1500 and 2000 rpms. Can feel it in my chest and my seat. First noticed about 3 weeks ago, but didn't cause particular alarm until the 2nd week when we took a 600 mile round trip, seemed to be a bit more pronounced on the way home. Now it's been another week, and it definitely is increasing intensity.

I know the balancers are inherent problems on these, but it also kinda makes sense that an rpm related vibration could be mounts that finally decided to quit. Seems odd that the increase in intensity would be advancing so quickly with the balancer verses larger rubber chunks that could be persuaded to "give up" with some heavy throttle and shifting action (just happened to do four 0-60 rips before the road trip).

Haven't touched the transmission, no major changes. Car has 196k.

Switched out the balancer. Fixed.

I guess I'll try to throw in some random tidbits of fun info.

This is for a 2000 mustang 3.8 V6
Externally balanced, so maybe 99-00
No visual signs while old pulley installed
Upon removal, rubber severely deteriated and counterweight had visually shifted 10-20 degrees compared to new
Crank bolt size is m14x1.50
Rented a harmonic balancer puller from O'Reilly
Rented an installer from O'Reilly
Both were needed
Boiled the new to wiggle it onto the crank nose, in addition to a LOT of tapping with rubber mallet. I had a metal cup about 6 inches tall that I was able to insert inside the pulley so that I could tap centrally. There is a RIDGE inside the channel about halfway down that's a couple thousandths smaller. It is a bitch to get past. It will feel like your keyway is not lined up. Use a sharpie to mark the tip of the crank as well as the outside of the balancer to ease lining up both from the outside, and if you stick your head in front of the pulley looking at the nose. I attempted to sand down the ID step to help with getting past it. Seemed to work. I was NOT able to get it on without the installer tool. Note, if anyone needs insight on how to effectively work the installer, shoot me an email Danielpwest@Hotmail.com. It's a bit wordy, but it will save your crank threads, I'm sure. Mine was vague with instructions and told me to use a 14mm wrench on a nut that was too big for my 24mm, AND deep inside the pulley.
Do your front seal at the same time. It's only a few bucks.
Once I felt close to bottoming the pulley, I switched to my old Crank bolt. You got a new tty, right? Set your torque wrench low, like about 50lb ft. This will tell you when it just contacts. Switch to your new bolt.
Torque to 120lb ft.

Be very. Very. Careful of your radiator while tapping, pulling, wiggling, and moving while holding tools. I pulled the new pulley off a few times to realign, and one of those times I had a flashlight in my hand and put a hole in mine. Yay!