The key to gasser towing is RPM. I had to relearn that when I ditched the PSD. My first 7.4 4x4 4.10s towed our former 8600lb TT to western MD and Myrtle Beach many times without issue. Hit the hills at 3000-3500 rpm and accelerate as you go. Below that, you may as well stop and have lunch. Our current 7.4 4x4 4.10s is pulling our 10K empty 5er just fine so far, but haven't tempted fate yet. We just got it in May, no long trips yet. The 5.7 in the 3500 will have the big trans and all of the cooler packages, so if you are going to stay in FL or other flat areas it wouldn't scare me. Single wheel will tow more, dually will tow better. Have you weighed your 5er yet?
