Goodyear has not made that tire in at least 5 years, so it may have harder rubber [ because of age], plus I run 5.5 to 6.25 lbs of pressure in our 190 mph JrFuel 225" WB car running 31x12x15 Goodyear [# D2585 light weight 22.6 lbs] on 12" rims. You may be running into tire shake running old hard tires with too much tire pressure.
BTW, the last 33x12x15 tire made is # 1288. Both of the D2585, & D1288 Goodyear tires, they have on a current do not build list, since 2012, but I had them make both on a special order, which I still have available.
Let me know if you want any more tire info or help,
Jon, 800-624-3803, 805-444-4489, cell