Hi: I am a new member with an aging Sierra 2500 4wd Duramax. I have had all the Duramax/Allison issues w/injectors/Prindle switches... and hopefully they won't recurr any time soon. I use this truck as a travelling toolbox- It has a Reading utlility bed/pony fuel tank, boss vplow. Rolling weight is 8000+lb. I have 135K mi and I was servicing it last night. I was suprised to see that upper ball joints (control arms) are loose- They were replaced @114K. I wonder why the replacements lasted only 20K? Is there a heavy duty replacement available. I did not change last ones myself but intend to do it this time. It doesn't look too difficult. Any advice is appreciated. Thanks.