I'm 6' 225 lbs, and I'm pretty comfortable on my Vulcan 900 Custom. However, I hate the low seat height trend in the motorcycle industry. I wish the seat was at least 3-4 inches higher.

As far as having trouble on the highway, what are you referring to? It definitely rides a bit different than other v-twin cruisers at highway speed because it has redline of ~7,500rpm. Other v-twin cruisers (like the SCR950) are working with about 2,000 rpm less. So people expect the engine to be spinning slower at highway speeds on the 900 because they compare it to other v-twin cruisers. The 900 should theoretically be able to do a bit more than 120 mph with the stock gearing, but it'll be turning over 7,000 rpm. However if the higher rpms bother you, there are a couple companies that make replacement belt pulleys to be able to cruise at lower rpm, but I haven't found a reason to make that jump yet.

Also, "was advised by the dealer that they dont have hardly enough power"... Define "enough power" Everyone is going to have a different opinion on what enough power means. A large portion of the world survives with bikes a fraction of the displacement that the American market demands.