2006 Toyota Tundra 4.7 crew cab 4x4 pulling a 1600lb Civic on a 900lb single axle trailer with a kart and other gear ~ 500lbs, so about 3000lbs total weight. I get 14-15 towing, 17 on hwy unloaded and 9-13 in town (my in-town consists of very short trips, so it is always low in any vehicle). I typically tow at the same speeds I would normally drive, so around 70mph. I haven't seen much sensitivity to speed, but we just got one of those scan tools at work that can track mileage, so I'm planning on doing some experimenting to see what the optimum speed/gear is.
Some other vehicles I've used to pull the same load:
1999 Chevy Astro - 16-17 towing
1993 Jeep Grand Cherokee Limited 4.0 4x4 - 12 towing
1999 Isuzu Rodeo 2wd - 15 towing
I've never had any scary moments with any of these trucks, but the Tundra is by far the most confidence inspiring truck I've used. It barely notices the trailer.
-Chris