We have done a lot of towing with our V-6. We have pulled a 6x10 enclosed trailer (~3500 lbs) from Minnesota to Colorado (through the mountains) without trailer brakes. The truck works hard but she does a good job. You really need to work the gears coming down the passes. Last summer, we towed our travel trailer (~3500lbs) from Minnesota to points all over the Rockies. Our camper does have trailer brakes and they are really nice to have. Since we are pushing it with this truck I added a tranny cooler and I use a sway control when towing these heaver loads. In high winds or steep grades, I need to kick it down to 3rd or even 2nd gear sometimes. My Toyotas have never let me down, so don't be afraid to push em!
That being said I finally pulled the trigger on a '07 V-8, since we do so much towing. I pick it up this weekend. It should be better yet!