Cat 3406e getting hot

I was wondering if I can get some help please. I have a 3406e on a 96 kenworth w900 that gets pretty warm . When parked at idle for 5 10 min, my coolant temp starts rising pretty fast. Also when I hit a small hill it also starts climbing pretty fast and this is while empty . This happens with fan off. When I hit my fan, it cools it down really fast at idle and when I hit a small hill.
I recently rebuild engine . New radiator and water pump. Before rebuild it was kinda doing same thing . Ended up rebuilding because I had 2 broken pistons. Throwing coolant tru overflow . I went from 190 to 180 to 170 thermostats . The 170 help a little but eventually will start rising . Any one have any clue why this is happening thank you

 

Would a clogged oil cooler do it? My oil temp always around 150 170

 

Before I rebuilt it I had a sensor thermo sensor that was set 195. One of the tabs broke off on top so I replaced it but I got a 205 one . My fan doesn’t come on at 205 . But I’m turning on fan manually . I plumed in a external gauge that I bought for autozone right into thermostat housing . It reads like 15 20 degrees hotter than the one on my dash

 

Yea that’s what I was thinking . But temp climbs fast when at idle and when I’m loaded or empty going on a small hill .