cooling problem

[Riskeman]

I've started having a cooling problem while cruising at highway speeds lately. When I'm in 5th and driving around 70 mph my temp will gradually increase from its normal running temps to hot. If I drop it into 4th to increase the RPM the the temp will drop back to its normal temp within 30 seconds. Also if I leave it in 5th and speed up to around 80 the temp will stay normal. Is this a problem with the water pump going out or not being turned at a high enough RPM?

 

[Blow-n-by-u]

Thermostat not opening up? :shrug:

 

[Cookieman00x]

Its hard to say, stock gauges arent that great. You best bet would be get a water temp gauge and that would tell you what the real temperature is.