Tachometer sweeps widely between shifts (5-speed) on 1997 Toyota Tacoma

Recently the techometer on my 5-speed standard shift 1997 Toyota Tacoma (2.7 four-banger) has been fluctuating by many more RPMs than usual between shifts. I suspect a slipping clutch. Is this the most likely diagnosis?

Asked by for the 1997 Toyota Tacoma
Sounds like a clutch problem alright but get it checked out before jumping to conclusions.