Hi

Car info:

2014 hyundai elantra gt

1.6L engine with 6 speed automatic transmission

120000 miles

bought brand new, I'm the single owner

most driving in city. 

Problem:

under acceleration specifically between 50 and 60 mph the body severly vibrates, steering wheel does not. driving at constant speed does not induce vibration, acceleration outside this speed range no vibration, and car moves in a straight line and does not pull right or left

Solutions tried so far:

1- Fixing bent wheel.

2- Alignment.

3- wheel balancing.

4- changing all shock absorbers.

5- changing engine and transmission mounts.

6- wheels rotation

I planned to change tires but thout I could ask first since they have life left in the threads, michilen primacy 4 with approximately 50000 miles and two years. what else should i consider as a source of this problem?