Hi lasagolf,
I have used Universal Androot on my HTC phone and have had no problems. It requires nothing special and can give you root access.
You don't need root access to tether using PdaNet however. I have used the free version for a while now. Maybe a couple of years. The paid version is pretty expensive compared to most Android apps but if you want to do HTTPS you have to have it.
I don't know if they work on Thunderbolt or not but they've always worked ok for me. In fact my less than dependable 4G hotspot wasn't working yesterday on 4G or 3G but my phone and PdaNet had no trouble at all.
Phyll