I have not had any issues with mine. Most I've had is 19klbs pulling a cattle trailer but that was only 15-20 mile runs.
Had lots of long runs with the bumper pull camper around 10-11klbs loaded down. Also have a 25' flatbed tandem but don't think I've loaded it heavy.
Biggest thing I noticed is the sidewall roll. They feel very wishy washy compared to a 10ply. Look at the max load psi, I think 55 on these extra load c ply and 80psi on 10ply. My cooper Zeon in the same size had a lot better sidewall support from what it felt. These nittos are just soft.
I'm happy with the nitto's though, for the price the have been very durable. I only get about 25k miles out of a set though, that part sucks. 305/50r20 on 9" rims