RV Cam

I just bought a 88 silverado with a rebuilt 350... the owner said when it was rebuilt he had an RV Cam put in it? Does this make much difference on power? and if so in what way?

Depending on the specs of the cam it can make quite abit of difference. RV cams tending to make the most improvements in lower rpm ranges giving more usable power and torque. The aggressiveness of the cam will determine the idle of the truck also. Bigger cams have rougher idle, so the smoother the idle the closer to stock and chance are the smaller the increase in power.

What exactly is an RV cam though? Just a name brand of cam or what?

It is a cam with a certain grinding (lift , duration) designed to make torque lower in the powerband and is mostly used for pulling.
Crane, Lunati, and several other brands offer "RV" cams.