I have the Marathon's also, but starting to have problems with them after about 17,000 miles on them. My trips are about 4,000 miles everytime we go. I know I am going to start something but my friends are telling me to go to LT. I ahave ST 23580R16 now. My trailer is just over 16,000 lbs. 37' Brookstone 5r
Don't really know if these are a lot better or not, but I am also pulling a heavy unit. I have GY LT 215/75R17.5 H load and keep them at 110psi. No problems so far.
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Bill & Pam
2014 Trilogy 3650RE
2015 F350 PSD