RPM fluctuates @ high speeds, spark plugs???

[runnert]

Hey all, Its just that when I am traveling highway speeds and I hit an incline, my RPM will jump up to around 3500 (2500 is normal at 75mph) . I havn't replaced my plugs for a few years and have traveled at least 50k since then. But this is the first time I have ever seen this happening. Otherwise, the truck runs as normal.

 

[BlackBII]

Do you have an Auto Tranny?

Is it maybe downshifting to make it up the incline?

 

[Big Jim M]

Sorry runnert but that ain't plugs! Plugs would cause a DECREASE in rpm. An increase in rpm is a change of gears by the auto tranny or slippage of the clutch if a manual.
Listen carefully and you should hear it change gears.
2500 at 75mph sounds a bit low to me. Also jumping a full 1,000 rpm sounds a bit too much to me...unless it changes 2 gears when it is shifting down.
Big JIm

 

[runnert]

Sorry to mention, it is a 5 speed.

I have kinda known that the tranny has needed a clutch also. This also sounds like a viable issue. It has 192k.