Steering Shakes like crazy!!

[Firstboxster]

Hello everyone- looking for some help on an issue that I haven’t been able to find while searching the forum anywhere. I own a 97 Base with 77k miles. The steering wheel shakes like crazy. I went to have it looked at last week and the inside edge of the right rear tire was worn bald to the threads. Was told that was probably my issue. I changed all 4 tires at that point to brand new Firestone Firehawk Indy 500’s along with a complete balance and full alignment and went on my way. Felt much better...for about 30 miles! Now the wheel is shaking again. The faster I go, the faster it shakes. Has anyone seen anything similar and corrected it?? Any advice?? Thanks in advance!!!