You say "started to rise" As one goes faster there is more heat in the engine.. The temp system in an engine is not rocket science. The temp changes from minute to minute slightly. Unless the coolant is puking out of the overflow the engine isn't hot.
But that said temp climbing as spped increases could easily be low coolant or poorly preforming viscus fan clutch.

Funny thing bout my Ranger.. The oil gauge is always either at zero (when off) or at halfway when running. I found there isn't a sending unit in the thing. Instead it has a switch that keeps the gauge at zero until reaching 7-1/2 lbs of pressure. At 7-1/2 lbs the switch closes and the gauge goes to halfway! Just a variation of the old idiot light. Makes the dash look good though.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />