I have a 6x12 that I tow with the runner. I've done a few short trips not on hwy no problem. I did one long trip from FL to TX with 3,000 lbs in the trailer. Like you said, I was barely able to keep 60 to 70. Then I got a 2nd gen SC with all the goodies. No doubt its better, but it isn't as good as I thought it was going to be. The upside, it doesn't downshift and upshift as much. It still struggles a bit, but its better than it was before. IMHO, its not worth it. Don't get me wrong, I love my 4runner but I advise you to trade up rather than sink the money into a SC. If you do it right you'll be into it $3-4K. Thats if you buy a used supercharger, do the valve cover gaskets, timing belt ect, plus fuel upgrades, and trans upgrade.