Detroit series 60 12.7 overheating

Hi folks, I'm running a 2000 Western Star 4964ex with a series 60. The truck comes close to overheating on the slightest hill and from leaving a stop sign/stoplight. Fan works, changed thermostats, new air filters, new coolant, and checked for obstructions everywhere I could. I plan to do a combustion gas test on the coolant tonight, but I'm looking for any help I can get. If you need more info, Just ask. Thanks in advance.

 

Heat gun and gauge both read within a few degrees of each other. I cleaned the radiator out as best as I could, but I'm leaning towards it being plugged or junk. The way it climbs to 220 is insane, but it cools down quickly when I stop and idle it, or just cruise along. Would that be a sign of a bad radiator or something worse?

 

I'd much rather do a water pump than a radiator lol

 

Would a water pump have any other symptoms? Fluids being contaminated and such? I think I'm going to change out both the radiator and water pump at the same time.

 

The more I think about it, the more the water pump makes sense. I honestly have no idea how old the water pump is on the motor to boot.