Inconsistent RPM?

I have a '98 Classic and I'm having a problem with my RPMs. When I floor the gas pedal, sometimes the tach will jump to only 3,000 and climb up from there while other times it goes straight to 4,000/4,500. Of course this makes a big difference in performance. A friend of mine thinks that the throttle body might have some gunk built up in it and it just needs to be cleaned. Figured I'd ask here before I go tinkering with the TB.

Anyone had this problem before? Any suggestions for a fix?

Thanks

If the vehicle bucks and jerks as it accelerates, the problem is probably a faulty throttle position sensor (TPS).