I don't know how helpful this will be, but thought I should get things started. As far as temperature goes, that sounds like normal operation to me. If you're riding at speed in 80 degree heat for any length of time, the temp is going to come up. Quarter of the range is not extreme at all.
As far as RPMs go, to my way of thinking the Vulcan is an older design, short-stroke motor. This bike likes to rev, and I don't think you're getting the best out of it by lugging it. In some ways this motor has more in common with say, an SV650 than a Harley. I try to keep the RPMs above 3k, and then only when cruising along at a lazy pace. Let that motor spin! Also 5k is not at all extreme, so that alone doesn't indicate any kind of problem. It's difficult to get a feel for what the problem is. . . .
Now, I was trying to get an idea if the clutch was slipping or if you are having fueling issues or what, then there's this unknown of oil level. Did you actually check your oil level (bike on center-stand, engine off--oil should at the top line in the sight glass behind the shifter)? Having too much oil is not good either, so you want to be sure you're helping the situation instead of making it worse. . . .
If the bike hasn't been ridden much recently, you might be having some issues with fueling. It sounds like the bike runs well enough most of the time, so chances are a fuel additive like Seafoam or Berrymans B12 Chemtool (my personal favorite), might help things. Is the bike sputtering and bucking? Or is it more an issue of not transmitting the power of the engine to the wheels?