Help with water pump/cooling question...

[gmc67swb]

My truck as of recently has had the temp starting to bounce up and down on the freeway...engine speed is about 2000-2100 rpm at 70mph.(160 t-stat) So I go and get a new t-stat 195*. Put it in and the temp sky rockets! The radiator is a Griffin aluminum unit. If I take the truck out of 5th gear on the freeway and put it in 4th at about 70mph (3000 rpm) the coolant temp drops and will stay low. At idle in the driveway the temp starts to climb past 200*. If I rev the motor to about 2100-2400rpm the temp will go to 190-195*. I've had this setup for quiet sometime with no issues. Do yall think my pump is going away on me? I've never had a pump do that. I've always had them start to leak out the weep hole in the bottom but never loose flow. Has anyone experienced something similar to this?***JUST A NOTE, I'VE TRIED 3 DIFFERENT T-STATS WITH NO LUCK AND THE RADIATOR IS FULL AND HAS NO LEAKS****