97 Cadillac deville only overheats on hills it has a new radiator, water pump and rad cap. it runs fine on flat roads and at idle rad fans kick on about 222 degrees.

The most common overheating problem with the Northstar engine is a blocked purge line. It's job is to purge air out of the cooling system.
There is a small diameter hose coming from near the top of the coolant tank,this is the purge line.
With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating.If the hose is clear, check for blockage at the nipple on the tank.Or trace the hose back until you find the blockage.The hose goes in to the engine to a crossover and comes out the other side to near the thermostat housing,the blockage may be there.

There's a few things I'd take into consideration. As stated in other posts, yes make sure transmission fluid is up to proper level. Also, depending on what engine you have, there may be an electric assist pump or even 2 in the system. On some, they have an electric pump to circulate coolant through heater core at idle to maintain proper heat , as well as another to assist mechanically driven pump when coolant temperature gets to approx 195F. Obviously when going up hills there is an added continuous load on engine, which will cause it to run hotter, thus I would expect that electric pump to be kicking in, and if not, may be the cause. Also the added load of climbing hills, creates added exhaust temperature, and if there is any restrictions, the results would be overheating. Quite often you may feel at least a little lack of power compared to what it used to be, or an increase in fuel consumption, or both when exhaust has a restriction. With that said, a weak water pump is also a possibility. Hope this sheds some light on what to pay attention to.

I'd check the transmission fuild level.