I put on a new RC steering stabilizer the other day to replace my stock one with 120,000 miles on it... and now I have some crazy death wobble at about 45. Why would I get death wobble after putting on a new heavy duty steering stabilizer?

What should I check next? My Track bar?

 

loose track bar.. bad trackbar bushings... tie rod like everyone else will say

 

Thats a first. most people incorrectly do the stabilizer as an improper fix for DW. you need to check everything, starting with the trackbar, also the ball joints, bushings, Tierod ends, steering box, alignment, tire balance, shocks.

 

and believe it or not. Even tire pressure. Yes tire pressure. Some service doh doh put my tire pressure at 42psi when I normally run at 30 or 32. that 10psi made a difference.
Start with the obvious places and least expensive.