Speedo sensor issues???

"Swap with a known good unit."

...because, the problem's either the speedo head, or, the sending unit, right? Either is very $pendy (and probably "nonreturnable electrical parts").

You got u-pull-it type yards in your locale? Go get a sending unit off the tranny. Or, swap with a "friend".

I am not familiar with Toyota names for the American market but my UK '94 Hilux truck can be affected by salt laden road dirt. The symptom is intermittent speedo operation with the needle swinging between zero and actual road speed. With the number of speed cameras operating here, this can be quite a worry.

A clean round the sender area appears to have cured the problem.

regards