The cheap, generic Chinese brand servos are known for their centering issues. The only way one of those would fix your problem would be pure luck; you get the 1 out of 100 that doesn't buzz and shake at center.

You're going to have to bite the bullet and buy a higher-quality servo for a truck that heavy. Something like an AE XP 1015 would work great in your vehicle. Otherwise, look at something from Savox but beware brownouts, i.e. use a glitch buster on your receiver from the start.